The physiologic disposition of the narcotic analgetic, alphaprodine (1), following iv adminstration in dogs conforms to a two-compartment, open-system model. The rapid disappearance of 1 from plasma and the large volume of distribution are in keeping with its rapid onset and short duration of action. The only extractable metabolite, noralphaprodine (2), achieved maximum plasma levels within 40 min after injection and remained constant for the duration (4 hr) of the experiment. The urine was found to contain 2 and conjugated metabolites whose identity presently is not known. Evidence is presented which suggests there is rapid equilibration between brain and plasma.