The technique of .gamma.-imaging can be used to study the deposition of 111In-labeled platelets onto synthetic arterial grafts in vivo. Platelet uptake on polytetrafluoroethylene (PTFE) grafts may depend on the choice of anesthetic. To evaluate the effect of anesthesia a series of experiments was performed in 7 dogs wherein each animal served as its own control. The 1st of paired femoral or carotid PTFE grafts was inserted with the animal under pentobarbital anesthesia, and the graft was imaged for 90 min. A 2nd graft was then inserted after at least 1 h of halothane anesthesia. The mean activity ratio (describing platelet deposition) in the grafts inserted when only pentobarbital anesthesia was used was 7.04 .+-. 0.55, compared to 1.20 .+-. 0.07 in the grafts inserted with halothane anesthesia (P < 0.01). Halothane anesthesia led to significantly decreased platelet uptake on canine PTFE arterial grafts. This effect was reversible, though not immediately, with no significant difference in graft activity noted by the day following surgery.