To examine the effects of short-term dietary lipid modification on alpha- and beta-adrenoceptor-mediated cardiovascular responsiveness, 19 normal volunteers consumed either a high-fat or a low-fat diet for 2 weeks in an open, randomized, crossover study of 6 weeks' duration. Diets were balanced for sodium and potassium content. Adrenoceptor-mediated cardiovascular responsiveness was assessed by measuring blood pressure and heart rate responses to incremental infusions of phenylephrine and isoprenaline. Baroreflexes were studied by examining heart rate responses to phenylephrine and to the Valsalva manoeuvre. Total plasma cholesterol and low-density lipoprotein cholesterol levels both fell significantly (by 22% and 26%, respectively), on the low-fat compared with the high-fat diet, as did resting supine blood pressures and heart rate (by 6 mmHg systolic and 3 mmHg diastolic, and 5 beats/min). These changes were accompanied by a significant reduction in the systolic blood pressure response to isoprenaline. Blood pressure responses to phenylephrine and baroreflex sensitivity did not change. These results suggest that dietary fat intake alters cardiac beta-adrenergic reactivity without significant effects on vascular alpha-adrenoceptor mediated responses or baroreflexes.