Neither the kinetics of the hydrophilic beta-adrenoceptor blocker atenolol nor those of the lipophilic metoprolol were influenced by the concurrent administration of amitriptyline. Compared with placebo, chronic administration (14 days) of atenolol and metoprolol (each as monotherapy) did not significantly reduce oxidative liver metabolism as measured by antipyrine half-life and by 6-beta-hydroxycortisol excretion. Compared with atenolol and metoprolol monotherapy, chronic administration of amitriptyline concurrently with each of the beta-adrenoceptor blockers produced an insignificant decrease (circa 10-20%) in antipyrine half-life and 6-beta-hydroxycortisol excretion. Amitriptyline appears therefore to have little enzyme-inducing activity.