8. Patients must have recovered from the toxic effects of prior therapy: 4 weeks from prior cytotoxic therapy and/or at least two weeks from vincristine, 6 weeks from nitrosoureas, 3 weeks from procarbazine administration, and 1 week for non-cytotoxic agents, e.g., interferon, tamoxifen, thalidomide, cis-retinoic acid, etc. (radiosensitizer does not count). Any questions related to the definition of non-cytotoxic agents should be directed to the Study Chair.