Thirty patients were entered in a phase I trial of aziridinylbenzoquinone (AZQ). These patients were treated with a single i.v. dose of AZQ daily for 5 days at doses ranging from 0.5 mg/m2 10.0mg/m2. The dose-limiting and only significant toxic effects were leukopenia and thrombocytopenia, which appeared with relative consistency at i.v. dosages of 4.0-4.5 mg/m2 per day .times. 5 in patients with extensive prior treatment and 7.0 mg/m2 per day .times. 5 in patients with little prior treatment. One patient with colon cancer achieved a partial response of 4+ mo. No other evidence of antitumor activity was observed. Pharmacologic studies revealed that the drug disappeared from the plasma in a biphasic manner (.alpha.-half-life = 1.5 min, .beta.-half-life = 18 min). With this method of analysis by high-performance liquid chromatography, no metabolites were found in the serum.