The pharmacokinetic properties of WR-2721 were investigated in 13 cancer patients given a 150 mg/M2 intravenous bolus dose of the drug. An average plasma clearance value of 2.17 L/min was obtained. Very little of the drug or the two metabolites, WR-1065 and WR-33278, were excreted in urine obtained after the blood collection schedule. Plasma concentrations of WR-2721 decreased by 94% within 6 minutes of drug administration. The mean value of 6.44 L obtained for the steady-state volume of distribution indicates that the extravascular space occupied by the drug is small. These observations suggest that in human cancer patients, WR-2721 is rapidly taken up by tissues and converted to metabolites.