BCNU is cytotoxic only at high concentrations in Neuro-2a (N2a) cells. A) LDH release was measured as an indicator of cytotoxicity after incubation with different concentrations of BCNU as indicated. BCNU was not toxic up to 20 μM and significant cytotoxicity was observed only at 80 μM (P < 0.01), and120 μM (P < 0.01). B) The MTT reduction assay also indicated significant toxicity only at 80 μM (69%, P < 0.01) and 240 μM (48.7%, P < 0.001) but BCNU was nontoxic up to 20 μM. For all samples, n = 4 ± SEM. **, P < 0.01versus untreated controls by analysis of variance (ANOVA) followed by post-hoc test by Dunnett multiple comparisons. BCNU, 1, 3 bis (2-chloroethyl)-1-nitrosourea; LDH, lactate dehydrogenase; MTT, 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide.