We investigated the pharmacokinetics of tranylcypromine, as well as the relationship between plasma levels of this agent and its effects on blood pressure and pulse rate. Tranylcypromine was absorbed rapidly after oral dosing, with the peak level being attained within 0.67 to 3.50 hours. Absorption was biphasic in seven of nine subjects. Elimination of tranylcypromine also was rapid, with a t 1/2 between 1.54 and 3.15 hours. From 2 to 7 hours after dosing, standing systolic and diastolic blood pressures were lowered and standing pulse was raised, compared with baseline. Onset of the effect on standing systolic blood pressure was correlated with the time of peak plasma tranylcypromine concentration. Maximum orthostatic drop of blood pressure and rise of pulse rate occurred 2 hours after dosing. Mean plasma tranylcypromine concentrations were correlated with mean orthostatic drop of systolic blood pressure and rise of pulse rate. Patients who have clinically significant hypotensive reactions to this agent may benefit from changes in their dose regimen aimed at minimizing peak tranylcypromine levels.