Ametantrone acetate is an intensely blue anthracenedione undergoing clinical trials in man. In this Phase I study, 20 patients received 39 courses of drug as a single IV dose given daily for five days and repeated every three weeks (21 days). Dosage escalations proceeded from 15 mg/m2 to 35 mg/m2. Predictable and reversible leukopenia was the dose limiting toxicity. One previously untreated patient with renal cell carcinoma metastatic to the lungs and right arm experienced a partial response of 51 days duration. Nine patients had pharmacokinetic studies performed during the study. Ametantrone was extensively distributed (apparent volume of distribution, 26.3 l/m2) and demonstrated a short half-life (harmonic mean half-life, 0.38 hour). The maximum tolerated dose in this study was 35 mg/m2. Recommended doses for Phase II trials are 30 mg/m2 in good risk patients and 25 mg/m2 in poor risk patients. Because of the partial response seen in one patient with renal cell carcinoma, Phase II trials should include this tumor category in order to better define the activity of ametantrone in this disease. In addition, since the total amount of drug that could be given to patients receiving the five day schedule (125-150 mg/m2) was approximately the same amount that could be administered as a single dose (140 mg/m2), it would appear that the only advantage of the daily times five day dosage schedule would be in the lower incidence of bluish skin discoloration.