Postoperative changes related to platelets and their correlation with the incidence of deep venous thrombosis (DVT) were studied in 30 patients undergoing total hip replacement. Levels of platelet count, platelet-crit, mean platelet volume, spontaneous platelet aggregation, platelet factor 4 (PF4) and β-thromboglobulin (β-TG) were measured before operation and on the 1st, 3rd and 7th postoperative days. DVT was detected by 125I-fibrinogen leg scanning in 11 of the patients. After the operation there was a significant and progressive increase (p < 0.01) in PF4 and-TG, and the presence of circulating platelet aggregates was demonstrated. Platelet count levels and platelet-crit were decreased on the 1 st and 3rd postoperative days followed by recovery on the 7th day. The changes observed following total hip replacement were not related to the development of postoperative DVT.