A phase II evaluation of anguidine was carried out in 30 patients with advanced refractory breast cancer. A dose of 5.0 mg/m2 daily for 5 days was explored. The main toxic effects were nausea and vomiting, fever and chills, hypotension, skin erythema, somnolence, confusion, and lethargy. Myelosuppression was minimal. Among these extensively pretreated patients, there was one partial responder and one additional patient who showed improvement (less than a partial response); both responses occurred in soft tissue sites.