Drugs. VP-16 was prepared by diluting fresh surplus stock solutions,
obtained from the ontology outpatient clinic, with 0.15 M NaCI. All
other drugs were obtained in powder form from the Division of Cancer
Treatment, the National Cancer Institute, Bethesda, Md. All drugs were
diluted to a concentration equal to 10 times the desired final concentration
in O. 15 M NaCI and stored at -70 ~ until use. Nitrogen mustard
was stable for 3 months when stored in this manner, as monitored by
cytotoxicity assays on established cell lines. Carmustine was unstable
at -70 ~ and was freshly prepared weekly. Drugs were sterilized by
filtration through 0.22-/~m pore diameter filters