The pharmacokinetics of N-2-(p-chlorophenoxy)-isobutyryl-N'-morpholinomethylurea (plafibride, ITA 104) in rats, and its intestinal absorption, plasmatic biotransformation, urinary elimination and fecal excretion were previously studied. 1200 mg of plafibride orally were administered to 5 healthy volunteers and then the presence of the drug and its metabolites was studied in the serum. The presence of unchanged plafibride and clofibric acid was detected, whereas that of 2-(p-chlorophenoxy) isobutyrylurea was not. At the same time the platelet antiaggregating activity of plafibride was investigated in the 5 volunteers. In this study plafibride presented a good and long-lasting platelet antiaggregating activity.