Didemnin B 6.3 mg/m2 was administered intravenously to 48 patients with recurrent or progressive central nervous system tumors. One patient of 39 (2.9%, 95% confidence limits 0.1 to 13.5) eligible patients had a confirmed partial response utilizing standard solid tumor criteria which lasted 14 months. Toxicity was significant. Nausea and vomiting and lethargy were the most frequent toxicities, but multiple severe toxicities were seen. Further investigation of Didemnin B at this dose is not warranted in patients with central nervous system malignancies.