Twenty-four femoral arteries in 12 rats were used to compare longitudinal and transverse closures in blood vessels approximately 1 mm in diameter. The closure techniques were applied to a simple longitudinal slit, 1 mm long, and to a longitudinal defect, 0.5 mm wide and 1 mm long. Comparisons were made of the change in pre- and postrepair flow velocities, recorded every 5 min using a 20-MHz pulsed Doppler velocimeter. Maximum reductions in flow velocity (linearly related to volume flow) were 10% and 29% for the longitudinal and transverse repairs, respectively, when applied to the longitudinal slit, and 65% and 19%, respectively, when applied to the larger arteriotomy. An analysis of variance indicates that the differences in the normalization of flow velocities during the immediate postrepair period are significant (P < 0.05). We conclude that optimal flow normalization is achieved by applying the longitudinal repair to the simple slit and the transverse repair to the larger arteriotomy.