methyl)phenothiazin-l0-yl]propyl]-l-piperazineethanol ester with heptanoic acid] in a sesame oil formulation was administered intramuscularly to dogs. Only traces of radioactivity were found in the circulation. Excretion was predominantly in the feces; 2-3 % of the dose was excreted in the urine. Radioactivity was still present at the sites of injection 21 days after the dogs had received the dose. Unformulated fluphenazine-14C enanthate was excreted according to a biphasic, exponential decay curve after intravenous administration to a dog with an externalized bile duct. The half-life of the slower portion of this decay curve was considerably faster than that observed in dogs that had received formulated fluphenazine-14C enanthate intravenously. Thus, the rate-limiting step in the biological disposition of formulated fluphenazine-14C enanthate after intramuscular administration is probably the release from an oily depot rather than excretion. Unformulated fluphenazine-14C enanthate, administered intramuscularly to a dog with an externalized bile duct, also represents a slow-release situation. Therefore, the sesame oil employed in the formulation serves as a convenient vehicle for the administration of the drug, although its presence is not an absolute requirement for slow release. Fluphenazine-14C enanthate is hydrolyzed to fluphenazine-14C by plasma esterases. Radioactivity present in the bile of a dog that had received fluphenazine-14C enanthate intravenously was identical with the glucuronide conjugate of 7-hydroxyfluphenazine. Thus, fluphenazine-14C enanthate appears to be metabolized by the dog according to the metabolic pathway established for fluphenazine-14C. Keyphrasa 0 Fluphenazine-14C enanthate-metabolism, excretion Biliary, urinary, fecal excretion-fluphenazine-14C enanthate I I ] Tissue levels-fluphenazine-W, metabolites 0 Metabolite-7hydroxyfluphenazine glucuronide 0 TLC-analysis 0 Scintillometry-anal ysis