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SUMMARY1. Observations were made upon five subjects who flew through 4j-6 time zones, four of them returning later to their starting point, and upon twenty-three subjects experiencing simulated 6 or 8 hr time zones shifts in either direction in an isolation unit.2. Measurements were made of plasma concentration of li-hydroxycorticosteroids, of body temperature, and of urinary excretion of sodium, potassium and chloride. Their rhythm was defined, where possible, by fitting a sine curve of period 24 hr to each separate 24-hr stretch of data and computing the acrophase, or maximum predicted by the sine curve.3. The adaptation of the plasma steroid rhythm was assessed by the presence of a sharp fall in concentration after the sample collected around 08.00 hr. The time course of adaptation varied widely between individuals; it was usually largely complete by the fourth day after westward, and rather later after eastward, flights. After time shift the pattern often corresponded neither to an adapted nor to an unadapted one, and in a subject followed for many months after a real flight a normal amplitude only appeared 2-3 months after flight.4. Temperature rhythm adapted by a movement of the acrophase, without change in amplitude, although on some days no rhythm could be observed. This movement was always substantial even on the first day, and was usually nearly complete by the fifth.5. High nocturnal excretion of electrolyte was often seen in the early days after time shift, more notably after simulated westward flights. Adaptation of urinary electrolyte rhythms usually proceeded as with temperature, but the movement of the acrophase was slower, more variable ANN L. ELLIOTT AND OTHERS between individuals, more erratic, and sometimes reversed after partial adaptation. On a few days there were two maxima corresponding to those expected on real and on experimental time.6. Sodium excretion was much less regular than that of potassium, but adapted more rapidly to time shift, so that the two often became completely dissociated. Chloride behaved much as sodium.7. The time course of adaptation of the plasma steroid and urinary potassium rhythms were sufficiently similar to suggest a causal connexion. The time course of adaptation of the temperature rhythm did not coincide with that of any other component considered here.

workers. Urine samples have been collected from day and night shift workers in a light engineering factory over periods of 24 or 48 hours during which blood was also collected for determination of plasma 11-hydroxycorticosteroids (11-OHCS). Different subjects divided their 24-hour output into as few as 4 or as many as 14 portions. Where possible, the timing of the excretory rhythms was assessed objectively by fitting a sine curve. The potassium excretory rhythm was, in most subjects, well adapted to night work in that they excreted least during their hours of sleep; no relationship could be discerned between potassium excretory and plasma 11 -OHCS rhythms. The sodium excretory rhythm was less regular than that of potassium in both night and day workers, and in night workers both sodium excretion and urine flow were often high during the hours of sleep, so that the subjects were sometimes awakened by the need to micturate. There was, however, sufficient association between the behaviour of sodium and potassium to suggest that their excretory rhythms have a common cause, and that this is not the secretion of 11-OHCS. Phosphate excretion fell sometimes on rising, even though plasma 11-OHCS concentration was not high, and sometimes after a high level of plasma 11-OHCS, at a time other than on rising. This suggests that these are two independent contributory causes of the usual morning fall in phosphate excretion.In our previous paper (Conroy, Elliott, and Mills, 1970) we compared the rhythms in plasma corticosteroid concentration of a group of night shift workers in a light engineering works with those of a group of day workers in the same factory. The subjects produced serial urine samples on the same occasions, and their electrolyte excretory rhythms are described in this paper.Subjects and experimental procedure The designation of the groups of subjects is the same as in our previous paper.Group la Eleven night workers were provided with 'Present address: Department of Physiology, Royal College of Surgeons in Ireland, St. Stephen's Green, Dublin 2. measuring cylinders and small bottles and were asked to record the time and volume of each urination over a period of 24 hours, and to provide us with a sample for analysis.Group lb Fifteen night workers, including three from group la, were asked similarly to collect serial urine samples over a period of 48 hours.Groups 2a and b Eight and 12 day workers in the same factory were similarly asked to produce urine samples over continuous periods of 24 hours and 48 hours.The frequency of voiding varied widely between subjects, so that we received as few as 4 or as many as 14 samples to cover a 24-hour period; some subjects failed to produce samples to cover the whole period requested, and a few samples were lost, so that we had information about the volume but not the composition. The number 356

. Circadian rhythms in plasma concentration of 11-hydroxycorticosteroids in men working on night shift and in permanent night workers. Blood samples have been collected for estimation of plasma 1 I-hydroxycorticosteroids from three groups of workers -day and night shift workers in a light engineering factory, and night workers in a newspaper printing works. Up to five samples were collected over 24 hr, or two samples per 24 hr were collected for three days. In conformity with the observations of others, day workers showed maximal concentrations in the morning around the time when they started work. In the newspaper workers maximal concentrations were found when they awoke around 14.00 hr. Night shift workers in the engineering works showed a greater variety of pattern, some showing the pattern usual in a day worker, some showing a maximum concentration about midnight and a minimum around 06.00 hr and a large proportion showing no clear circadian rhythm.In the newspaper workers the rhythm was thus well adapted to their pattern of nocturnal work, whereas relatively few of the night shift workers in the engineering works showed such adaptation. It appears that the adrenal cortical rhythm can be adapted to night work in a community in which this is universal, accepted and lifelong, but that such adjustment is unusual in men on night shift work for limited periods, and whose associates are mainly following a usual nycthemeral existence.