Piroxantrone is an anthrapyrazole compound undergoing phase II testing in a variety of diseases. The anthrapyrazoles are a series of compounds synthesized with the intent of maintaining the broad antitumor activity of anthracyclines, but with lessened cardiac toxicity. The Southwest Oncology Group (SWOG) conducted a phase II trial of piroxantrone in advanced soft tissue sarcoma. Treatment consisted of piroxantrone 150 mg/M2 administered intravenously over 1 hour every 21 days. Twenty-five eligible patients were registered to the trial. Twenty-three patients received treatment and are fully evaluable for response and toxicity. Two partial responses were seen for an overall response rate of 9% (95% confidence limit 1%-28%). Abnormal cardiac ejection fraction occurred in five patients, and fatal congestive heart failure developed in one patient on study. Toxicities other than cardiac were tolerable. Based on the observed response rate and cardiac toxicity, further trials of piroxantrone in the treatment of soft tissue sarcoma do not appear warranted.