Policosanol is a new drug whose cholesterol-lowering effects have been demonstrated in experimental models, healthy volunteers, and patients with type II hypercholesterolaemia. The effect of policosanol on platelet aggregation was investigated in a randomized, placebo-controlled, double-blind study conducted on healthy volunteers. This included a trial of the effects of single doses (5 to 50 mg) and a study of the effects of repeated doses administered for 7 days. In the single-dose study, the percentage of platelet aggregation in response to the threshold concentration of ADP and epinephrine measured from 8:00 to 10:00 increased significantly in the placebo group, while policosanol (5, 10, 25 and 50 mg), administered orally, inhibited the increase of platelet aggregation induced by ADP and epinephrine determined at the same time. Policosanol administered at 20 mg/day for 7 days significantly inhibited platelet aggregation induced by ADP and epinephrine, although the inhibition reached by the 10 mg/day dose tended to be less significant (p = 0.06). A modest effect (p = 0.068) on collagen-induced platelet aggregation was only observed at the highest dose (50 mg/day). The low dose (5 mg/day) was ineffective. Policosanol did not affect the coagulation time when administered at single or repeated doses. No side-effects were reported in treated or placebo groups.