In order to study in its protective effect against post-operative thrombosis, Ticlopidine was administered to one out of two randomized groups of patients undergoing suprapubic prostatectomy. Bleeding time, platelet function, and haematological parameters were followed. Blood loss during operation and post-operatively were estimated, transfusions required and subjective tolerance were recorded. Among twenty-six evaluated patients receiving Ticlopidine, positive leg scans were found in four, whereas among twenty patients treated with acenocoumarol post-operatively, positive leg scans were found in seven patients. The difference is not statistically significant, thus Ticlopidine appears to offer a protection against deep venous thrombosis comparable to that of acenocoumarol. A score is introduced for comparison of the results of aggregation tests. Platelet aggregability diminished during the use of the drug, but the adhesiveness was not influenced by Ticlopidine. The bleeding time was prolonged in both groups studied. Ticlopidine did not raise per-operative blood loss and caused only slightly more haematuria post-operatively. The subjective tolerance was good.