Based on the activity of menadione (M) in the human tumor stem cell assay, we conducted a phase I trial of M in patients with advanced cancer. Forty patients (19 men, 21 women) were treated with 90 courses of M; 82 treatment courses are evaluable for toxicity. The median patient age, Karnofsky performance status, and number of prior chemotherapy regimens were 61 years (range 32-74 years), 80% (range 50-100%), and two, respectively. M was given by a short (1-5 h) intravenous infusion every 3 weeks, starting at 40 mg/m2 and escalating by modified Fibonacci scheme to 1360 mg/m2. Toxicity was graded according to the Southwest Oncology Group toxicity scale with defined hypersensitivity reaction (HSR) scales. No grade > or =2 hematologic toxicity was observed. Non-hematologic toxicity consisted of a HSR syndrome of paresthesiae of the extremities, facial flushing, burning of the eyes and mucous membranes, chest pain and dyspnea. HSR was defined as Grade I toxicity by the presence of facial numbness, flushing, and/or a tingling sensation or burning of the eyes and mucous membranes. Grade II toxicity was defined as the presence of the same above symptoms plus chest tightness, paresthesiae of extremities and/or dyspnea and chest pain. These toxicities were grade 1 in 3 of 4 patients at a dose of 840 mg/m2. At 1360 mg/m2, 2 of 13 patients suffered grade 1 HSR and 7 of 13 grade 2 HSR. No objective partial or complete responses were observed. Plasma menadione concentrations peaked at 1.9-7.4 microM during the infusion in 3 patients receiving 1360 mg/m2. Further phase 1 and 2 combination trials using longer infusion durations have resulted from this trial.