Flunitrazepam (FNZ) is a benzodiazepine derivative more potent than diazepam. FNZ abuse in the US has emerged in the last few years and has a growing popularity among young people and drug abusing populations. Ethanol (EtOH) consumption with FNZ enhances euphoria and onset of action. It is postulated that FNZ and EtOH cause liver cell injury. In this study, hepatocytes are employed to study the hepatotoxicity of FNZ, EtOH and their combination (FNZ-EtOH). Hepatocytes (2x10(6) cells/ml) isolated from male Sprague-Dawley rats were exposed to saline, FNZ, EtOH or FNZ-EtOH in combination. The uptake of 0.4% trypan blue and the leakage of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) enzymes into the incubation media were used to assess cell membrane damage of hepatocytes. Where metabolism of FNZ is nearly complete through several hepatic pathways, animal pretreatment with Phenobarbital was used to study the effect of microsomal enzyme induction on cellular injury. FNZ (0.16mm), EtOH (32.56mm) or their combination caused a significant (P<0.05) decrease in cell viability. Compared with control, FNZ and FNZ-EtOH in combination caused significant AST leakage over the 2-hour incubation period. EtOH alone caused significant AST leakage after 2 hours of incubation. The leakage of ALT enzyme was significant for FNZ, EtOH and FNZ-EtOH over the 2-hour incubation period. While FNZ alone did not produce any significant enzymatic leakage in the Phenobarbital pretreated groups, the leakage of ALT and AST were significant for FNZ-EtOH in combination as early as 30 minutes of incubation. A significant depletion (P<0.05) of glutathione (GSH) was observed for EtOH and FNZ-EtOH in combination treated samples. This investigation suggests that FNZ and EtOH cause hepatotoxicity, and their combinations have an additive effect in increasing liver toxicity. Induction of microsomal enzymes revealed that FNZ is more hepatotoxic than the metabolites. And FNZ alone has no effect on GSH content.