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With the advent of newer leads to the electrocardiogram it has become necessary to repeat the observations that have been made in the past on the cardiographic changes following digitalis administration in healthy subjects. The main object of this work has been to determine the lead or leads most susceptible to the effects of digitalis as well as the design of the deformity produced in the tracing. The need for the investigation has arisen from the common practice of giving digitalis to a patient considered to have heart disease before the electrocardiogram is recorded as part of a special examination. Confusion in diagnosis is specially likely if chest pain is included among the symptoms-a circumstance that allots more than ordinary importance to changes in the electrocardiogram.Methods. The dosage of digitalis leaf was that customarily used in the continuous treatment of a patient needing it. It was, therefore, given in the first place as 2 grains (0-13 g.) daily and later increased to 3 grains (0-2 g.) daily. Rapid digitalization was not followed. Thirteen healthy medical students volunteered to take digitalis during a period of six to eight weeks when the total dosage was from 104 to 135 grains (6 9-9 g.). Digitalis was dispensed to each student when he attended the Cardiac Department to ensure accuracy in regard to the amount taken. A preliminary electrocardiogram was taken before the start of digitalis therapy and subsequent tracings were taken at intervals of four to ten days, and again after digitalis had been discontinued in order to discover the time it took the tracing to recover. The leads used included the four bipolar limb leads I, II, Ill, and IIIR (lead III during deep inbreathing) and the three chest leads CR1, CR4, and CR7. The tracing was recorded by an Elmqvist machine with the subject in the reclining posture and a standardization of 1 cm. from 1 mv. was strictly followed. RESULTSNo toxic symptoms appeared in any of the students during the period of medication. In the analysis of the results information was specially sought in regard to four problems. First, the smallest dose of digitalis that produced noticeable changes in the electrocardiogram. Secondly, the amount of digitalis that produced changes that could only be told by comparison of two records; this information has no great value in practice when only a single electrocardiogram is available at the time, and most papers on the cardiographic effects of digitalis deal only with the findings obtained from a comparison of two tracings. Thirdly, the particular deformity that signalled the earliest digitalis effect. Fourthly, the period needed for such changes to disappear and allow a return of the tracing to its normal design.The results will now be discussed under two heads dealing separately with the lesser and the more noticeable cardiographic changes.