Soluble P-selectin and whole blood aggregation (WBA) were measured after percutaneous coronary intervention in patients who then received antiplatelet therapy. One had subacute thrombosis on day 7. This patient's WBA exhibited time-dependent enhancement. In addition, the accentuation of WBA on day 3 was observed when anti-alpha(IIb)beta(3) antibody was added. The remaining 22 patients were divided according to WBA results on day 3 with anti-alpha(IIb)beta(3) antibody added (A group, WBA enhanced; B group, WBA did not enhance). WBA on day 3 was similar in the two groups. The ratio of WBA with and without anti-alpha(IIb)beta(3) antibody was higher in group A than in group B. A significant time-dependent increase of soluble P-selectin was observed in the A group. These results suggest that enhancement of WBA with anti-alpha(IIb)beta(3) antibody after percutaneous coronary intervention predicts subacute thrombosis.