Reports of pulmonary hypertension in obese women treated with the appetite suppressant aminorex (Menocil) prompted this study using the calf as a model because of its very reactive pulmonary vascular bed. Acute and chronic haemodynamic effects were observed following daily intravenous injections of aminorex (0·25 mg/kg as free base) in four calves. Four other calves were similarly treated with the related sympathomimetic drug amphetamine in the same dose, and four calves served as controls. The acute effects of both these drugs were a significant increase in systemic arterial pressure and resistance with no change in pulmonary haemodynamics. The chronic effect of one month's treatment was to leave both systemic and pulmonary haemodynamics unchanged, and there was no depletion in endogenous catecholamines as measured by the tyramine test. In addition, the reactivity of the pulmonary vascular bed to hypoxia remained unaltered. Thus neither aminorex nor amphetamine produced pulmonary hypertension during one month's treatment in the calf.