Although low molecular weight dextran is commonly utilized in clinical microsurgery, few experimental data are available documenting its efficacy. Bilateral 2-mm arterial inversion grafts were constructed in the femoral arteries of New Zealand White rabbits. The experimental group (n = 40 grafts) received a 5-day constant infusion of intravenous dextran 40 at 2.1 ml/hour, and the control group (n = 50 grafts) received no infusion. Whereas 85 percent (34/40) of the dextran grafts were patent at 1 week, only 48 percent (24/50) of the control grafts were patent (p = 0.0003). Scanning electron micrographs revealed a decrease in both platelet and fibrin deposition in the patent dextran arterial inversion grafts versus the patent control specimens. As a marked diminution in microvascular thrombosis was demonstrated at a clinically relevant dose, the continued use of intravenous dextran 40 in clinical microsurgery is supported by this study.