Platelet deposition contributes to the thrombotic and embolic complications of prosthetic materials in man. To determine if the investigational platelet inhibitory drug suloctidil (200 mg 3 times daily) reduces platelet deposition on Dacron aortic grafts, a randomized, double-blind, crossover trial was conducted in 12 men with grafts that had been in place more than 9 months. Platelet deposition in the graft was assessed by quantitative analysis of planar images obtained at 24, 48 and 72 hours after injection of indium-111-labeled platelets. Also, a tomographic method of imaging and quantitating labeled platelet deposition in the graft was developed. Tomographic imaging was performed at 24 and 72 hours after platelet injection and was quantitated by a graft/blood ratio that compared indium-111 platelet activity in summed 1.8-cm-thick transaxial tomographic slices of the aortic graft to indium-111 platelet activity in well-counted whole blood. Compared with placebo, suloctidil failed to decrease the tomographic graft/blood ratio at 24 hours (6.2 +/- 1.3 vs 5.7 +/- 0.8) and 72 hours (11.4 +/- 2.9 vs 10.7 +/- 2.2). Similarly, the graft/blood ratio determined by planar imaging was not different between placebo and suloctidil therapy at 24 hours (1.7 +/- 0.3 vs 1.6 +/- 0.2), 48 hours (2.2 +/- 0.4 vs 2.4 +/- 0.4) or 72 hours (2.6 +/- 0.5 vs 2.8 +/- 0.5) after labeled platelet injection. Thus, suloctidil does not significantly reduce platelet deposition on chronically implanted Dacron grafts in humans.