Vein graft flow (VGF) in response to peripheral venous administration of sodium nitroprusside (SNP) or diazepam was studied in 13 anesthetized patients following cardiopulmonary bypass for aortocoronary vein bypass graft operations. SNP (0.5 microgram/kg/min) significantly reduced mean arterial pressure (p less than 0.05). VGF paralleled the decreased blood pressure, but the reduction was not significant (p greater than 0.05). Diazepam (0.1 mg/kg) did not significantly alter blood pressure or VGF. We conclude that peripheral venous administration of SNP or diazepam is not a pharmacologically reliable method by which to increase VGF in the period immediately following a graft operation.