A survey of in vitro cytotoxic effects of camptothecin in human epitheliod sarcoma, colon, breast and ovarian carcinomas, glioblastoma, and neuroblastoma (PNET) cell lines, was done. We chose the MTT assay to measure survival and observed that 24 h exposures to camptothecin caused consistently greater toxicity than 1 h exposures. The LD50 for camptothecin was in the 12.5-25 ng/ml range. There was a 10-fold range of growth rates measured by OD after 5 days exposure and varied expression of MDR1 in these cell lines--none of which could be correlated with tumor sensitivity to drug. The most sensitive cell lines were colon and glioblastoma, and the most resistance were ovarian, breast and epithelioid sarcoma.