The effect of established infection with penicillin-resistant Staphylococcus aureus on microarterial and microvenous anastomosis was studied in a rat experimental model. The infection was treated with wound debridement and systemic antibiotics at the time of the surgical procedure. It was found that the patency rate of microarterial repairs at 10-14 days was 95.1%. Veins were less resistant to infection than arteries. Two types of vein involvement were found. These were classified according to the degree of thrombosis resulting from endophlebitis. The patency rate of anastomoses performed on the more mildly infected veins was 56.5% and that on the more severely infected veins was 0%.