In order to establish any psychotropic effects of the angiotensin-converting enzyme inhibitor enalapril, the drug was administered in doses of 20 mg every morning for 14 days to 12 normal subjects, and compared with placebo on a battery of physiological, psychological and subjective tests, before and after the dose on the 1st and 14th days. Diastolic blood pressure was significantly reduced and heart-rate increased by enalapril as compared with placebo; one component (P1-N1) of the auditory evoked EEG response was increased and tapping rate quickened. The commonest side effect was tiredness. It was concluded that enalapril (unlike most other antihypertensive agents) did not lower mood but could enhance attention and alertness.