Cannabidiol (CBD) has been shown to inhibit mouse hepatic mixed-function oxidations of several drugs after acute treatment, whereas repetitive treatment resulted in the restoration of drug-metabolizing capabilities. We have found that acute CBD treatment modestly decreased cytochrome P-450 content but markedly decreased hexobarbital hydroxylase, erythromycin N-demethylase, and 6 beta-testosterone hydroxylase activities. Repetitive CBD treatment, on the other hand, resulted in the restoration of cytochrome P-450 content as well as hexobarbital hydroxylase and erythromycin N-demethylase activities. However, after such repeated treatments a fresh dose of CBD can once again inactivate erythromycin N-demethylase activity but not hexobarbital hydroxylase activity. The resistance of hexobarbital hydroxylase to re-inactivation by CBD was paralleled by stimulation of pentoxyresorufin O-dealkylase activity and the appearance of a 50 kD protein that was immunoreactive to an antibody raised against rat hepatic cytochrome P-450b. CBD metabolism in vitro by microsomes prepared from such CBD-"induced" animals, resulted in a pattern of metabolites different from that observed from comparable incubations with liver microsomes from either untreated or phenobarbital-treated animals. Thus, it appears that CBD initially inactivates at least one cytochrome P-450 isozyme, but after repetitive CBD treatment, an isozyme is induced that is resistant to further re-inactivation by CBD. This isozyme appears to be immunochemically similar to, but somewhat functionally distinct from, the isozyme induced by phenobarbital treatment in mice.