Disulfiram is a drug widely used in the treatment of alcohol abuse. We have shown that a single disulfiram dose inhibits the activity of cyclochrome P4502E1. This effect of disulfiram has now been widelyused to show the involvement of P4502E1 in the metabolism of several drugs, and to decrease or prevent toxic drug effects caused y P4502E1-mediated metabolite formation. Although disulfiram is highly selective against P4502E1 in vitro, and single-dose disulfiram is highly effective against P4502E1 in vivo, the specificity of single-dose disulfiram for only P4502E1 in vivo in humans is unknown. Before disulfiram can be recommended to prevent toxic drug effects, its safety, vis-a-vis absence of unwanted drug interactions, must be demonstrated. This investigation will assess the effects of single-dose disulfiram on the in vivo activity of P450s 2C9, 2C19, 2D6, and 3A4 in humans.