Cylindrospermopsin (CY) is a newly isolated alkaloid produced by the cyanobacterium Cylindrospermopsis raciborskii, which has been linked to an outbreak of hepatoenteritis in man. The current work examined the suitability of primary cultures of rat hepatocytes as an in vitro model for studying the cytotoxicity of CY. We found that CY (3.3-5.0 microM) caused significant cell death (40-67% of cells by LDH release) in cultured hepatocytes after 18 hr incubation. While investigating possible mechanisms for CY toxicity, we found that lower, nontoxic doses of CY (1.6-2.5 microM) decreased cell glutathione (GSH) to about 50% of control. For toxic doses (5 microM), the loss of GSH preceded the onset of toxicity by six hr. Lowering cell GSH predisposed cells to CY toxicity. In conclusion, cultured hepatocytes are a suitable model for studies of CY cytotoxicity and GSH is involved in the detoxification of CY.