AnvirzelTM is an aqueous extract of the plant Nerium oleander which has been utilized to treat patients with advanced malignancies. The current study reports a phase 1 trial to determine the maximum tolerated dose (MTD) and safety of AnvirzelTM in patients with advanced, refractory solid tumors. Patients were randomized to receive this agent by intramuscular injection at doses of 0.1, 0.2, 0.4 ml/m2/day with subsequent patients receiving 0.8 or 1.2 ml/m2/day sequentially. Eighteen patients were enrolled and completed at least one treatment cycle of three weeks. Most patients developed mild injection site pain (78%). Other toxicities included fatigue, nausea, and dyspnea. Traditional dose limiting toxicity was not seen, but the MTD was defined by injection volume as 0.8 ml/m2/day. No objective anti-tumor responses were seen. Anvirzel™ can be safely administered at doses up to 1.2 ml/m2/day, with the amount administered intramuscularly limited by volume. The recommended phase II dose level is 0.8 ml/m2/day.