To determine if sulfinpyrazone inhibits platelet deposition on chronically implanted (greater than 9 months) Dacron aortic bifurcation grafts in man, we performed indium-111 platelet imaging over 24 to 96 hours after labeled platelet injection in 10 males with grafts before and during sulfinpyrazone therapy (200 mg four times daily). Platelet accumulation was quantitated by a graft/blood ratio that compared indium-111 platelet image activity in the graft to platelet activity in well-counted whole blood. In addition, independent visual analysis compared platelet accumulation in the graft area to adjacent native arteries. By quantitative evaluation, sulfinpyrazone did not decrease the graft/blood ratio compared to baseline at 24 hours (3.2 +/- 0.4 vs 3.3 +/- 0.5, mean +/- SEM), 48 hours (4.6 +/- 0.6 vs 4.6 +/- 0.9) , 72 hours (6.8 +/- 0.8 vs 6.7 +/- 1.3), or 96 hours (9.7 +/- 1.6 vs 9.7 +/- 1.6) after labeled platelet injection. Visual interpretation also revealed no decrease in deposition in any patient during sulfinpyrazone therapy. We conclude that sulfinpyrazone does not inhibit platelet deposition on chronically implanted Dacron arterial graft surfaces in man. The techniques described provide a useful method of evaluating antithrombotic drug effects in patients with intravascular prosthetic materials.