A phase I study of a new ergot alkaloid drug, mergocryptine (CBM 36-733), was carried out. Mergocryptine possess centrally dopaminergic, serotonergic and cholinergic actions and is anticipated to improve cerebral function. The phase I study was conducted in subjects who gave informed consent at a Clinical Pharmacology ward of Kitasato Univ. An initial dosage of the phase I study was determined referring to the conventional dose-finding method of phase I studies and to the dosages of overseas clinical studies. The initial dosage of 0.2 mg was increased to 0.4, 1.0, 2.0 and 4.0 mg on the basis of each laboratory test result and clinical symptoms at each step. At each step, two of the subjects were given inactive placebo. The subjects were divided into two groups, one for 0.2, 1.0 and 4.0 mg, and the other for 0.4 and 2.0 mg. Clinical pharmacological action Heavy-headedness, feverish abdomen, nausea, light-headedness and nasal occlusion appeared at a dose of 1.0 mg. The incidence and degree of severity rose as the dosage was increased. The duration was prolonged as well. Laboratory findings A physical examination revealed significant decreases in blood pressure at a dose of 4.0 mg, and pulse rate suggested that some subjects had mild bradycardia. However, body temperature was not affected. Mergocryptine did not display any effect on general urinalysis, blood count or biochemistry. In endocrinological test, prolactin was lowered in all the subjects from a minimum dose of 0.2 mg. TSH, T4 and LH were lowered as the dosage increased, but T3, GH or HCG were not affected. In physiological test, mergocryptine did not display any effect on ECG. EEG was carried out at a dosage of 2.0 mg, and slow wave of the basic activity was noted in one subject probably due to drowsiness, but no obvious influence of the drug was found. Funduscopy was not affected. No specific effects of mergocryptine were observed throughout the whole process of tapping test. Clinical pharmacokinetics Pharmacokinetics could not fully investigated because many of the data obtained were under the detection limit and there were big individual differences.