Streptozotocin, a nitrosourea, has limited antitumour activity. However, in concentrations and exposures higher than those achieved after intravenous dosing, streptozotocin has been reported to sensitize various cell lines in vitro to other nitrosoureas or alkylating agents. We hypothesized that the intraperitoneal administration of streptozotocin would achieve concentrations and exposures in the peritoneal cavity sufficient for this sensitization to take place. The pharmacokinetics of streptozotocin in the peritoneal cavity and in plasma were determined in patients who received 1 g of streptozotocin via the intraperitoneal route. Fifteen courses were administered to 12 patients. The mean total area under the concentration versus time curves (AUC) was 183 +/- 31 (SE) mM min in the peritoneal cavity (5 courses) and 5.3 +/- 1.1 (SE) mM min in plasma (6 courses). The mean peritoneal to plasma AUC ratio was 64 +/- 23 (5 courses). The mean peak streptozotocin concentrations in the peritoneal cavity (5 courses) and plasma (6 courses) were 1.9 +/- 0.4 mM and 0.03 +/- 0.01 mM, respectively. No significant toxicity was observed on any course. We conclude that intraperitoneal administration of streptozotocin is feasible, and that drug concentrations and exposures are in an appropriate range in the peritoneal cavity to cause sensitization to other nitrosoureas.