The aqueous root extract of Cryptolepis sanguinolenta (CSE) is a popular antimalarial in West African ethnomedicine. Cryptolepine (CLP), the major alkaloid of the plant, is a cytotoxic DNA intercalator that has promise as an anticancer agent. To date the aqueous root extract, the traditional antimalarial formulation, has not been evaluated for toxicity. In this study, we have examined the in vitro toxicity of CSE and CLP using V79 cells, a Chinese hamster lung fibroblast frequently used to assess genetic toxicity, and a number of organ-specific human cancer cell lines. CSE and CLP caused a dose- and time-dependent reduction in viability of the V79 cell line. Flow cytometric analysis of CSE- and CLP-treated (24 h) asynchronously growing V79 cells using propidium iodide (PI) staining revealed an accumulation of cells (up to 55%) in the sub-G1 phase of the cell cycle, indicative of cell death. The V79 cells and almost all the organ-specific human cancer cell lines exposed to CSE and CLP were profoundly growth inhibited, as measured in a clonogenicity assay. In a V79 cell mutation assay (hprt gene), CSE (5-50 microg/ml) only induced mutation at the highest dose employed (mutation frequency approximately 4 and 38 mutant clones per 10(6) cells for control and CSE, respectively), but CLP (0.5-5.0 microM) was not mutagenic. These results indicate that CSE and CLP are very cytotoxic and may be weak mammalian mutagens and/or clastogens. The poor genotoxicity of CSE and CLP coupled with their potent cytotoxic action support their anticancer potential.