A 3 × 10-cm dorsal rat skin flap contains a distal portion that is poorly perfused. The dorsal flap served as a useful model to test hemodynamic properties of the vasodilatory drug chlorpromazine. A control group of flaps were treated with saline and the test group with chlorpromazine (15 mg/kg intraperitoneally). Eight days postoperatively, the surface area of the flaps that necrosed was 27.3% for the treated group and 36.5% for the controls. Using Student's t-test this difference was significant (p <0.001). Nutrient blood flow determined by the penetration of fluorescein dye into the flap was consistently greater in the chlorpromazine-treated group compared with the control group in the first 24 hours postoperatively. The adenosine triphosphate (ATP) levels measured at 0 and 24 hours postoperatively were consistently lower in the distal parts of the flap, treated or control, compared with proximal parts of the flap (p <0.001, analysis of variance). However, there were no significant differences in ATP levels between treated and control biopsies at any one site on the flap. In conclusion, chlorpromazine had a beneficial effect on rat skin survival, and increased blood flow appears to be one of the major reasons.