The ability of phenobarbital (PB) to induce a "pleiotropic response" which includes both cytochromes P450 (CYP) as well as other drug-metabolizing enzymes was investigated in mice, rabbits, hamsters, and various inbred strains of rats. PB induced similar drug-metabolizing enzymes (CYP2B, CYP3A, and epoxide hydrolase) in rats, mice, rabbits and hamsters. PB and two structural analogues (ethylphenylhydantoin and barbital) induced a variety of drug-metabolizing enzymes (CYP2B, CYP3A, CYP2A, epoxide hydrolase) in a series of inbred strains of rats. In contrast, levels of aldehyde dehydrogenase (ALDH) (propionaldehyde, NAD+) which were expressed constitutively in all strains of rats were induced by PB in only two of the eight strains (ACI, Copenhagen). Further investigations of ALDH induction by structurally diverse compounds in Copenhagen rats demonstrated a strong correlation between the induction of ALDH and other elements of the pleiotropic response (CYP2B, CYP3A, epoxide hydrolase). These results imply that induction of ALDH (propionaldehyde, NAD+) is associated with the PB pleiotropic response in Copenhagen rats.