The mini-Wright peak flow meter (MPFM) has been evaluated, and the results obtained from it show a strong positive correlation (r= 0-970) with the Wright's peak flow meter (PFM). MPFM measurements, however, were biased to be about 38 1/min higher than PFM measurements (95% confidence limits 31[0 1/min to 450 1/min). Between instrument variation was found (F-ratio 3 67 with 9 and 81 degrees of freedom: P<0 001). In practice this did not appreciably affect individual measurements greatly as 95% confidence limits on any individual measurements were increased from 241/min to 271/min. There was no significant day-to-day variability in measurements obtained with individual instruments. The MPFM is a pocket-sized, simple, cheap, and robust instrument for following changes in ventilatory function. In clinical trials and surveys, however, both the bias in favour of the MPFM compared to the PFM and inter-machine variation must be taken into account. As the manufacturers have altered the scale to remove the bias since this study was performed, it will be important to know whether the original or the modified meter is being used in future studies.

Fourteen patients with the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) have been treated with demethylchlortetracycline (demeclocycline) 1200 mg daily. In 12 patients the underlying lesion was malignant. The serum sodium returned to normal (> 135 mmol/l) in all patients after a mean of 8-6 days (SD+5-3 days). Blood urea rose significantly from the pretreatment level of 4-2±2-3 mmol/l to 10-1±5-1 mmol/l at ten days (p<0 001). The average maximum blood urea was 13-4-6-8 mmol/l. In four patients the urea rose above 20 mmol/l, and in two of these demecyocycline was discontinued because of this rise. The azotaemia could be attributed to a combination of increased urea production and a mild specific drug-induced nephrotoxicity. Discontinuation of demeclocycline in six patients led to a fall in serum sodium, in one case precipitously, and return of the urea towards normal levels. Demeclocycline appears therefore to be an effective maintenance treatment of SIADH, and the azotaemia that occurs is reversible and probably dose dependent.

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