The bioactivation of the morphine prodrug, morphine-3-propionate, has been evaluated by determination of the first-order hydrolysis rate in different tissue homogenates and blood fractions from various mammal species, including man. The hydrolysis rates were determined in whole blood, serum and plasma from rat, rabbit and man, in serum from pig, in liver, kidney, brain, buccal mucosa, muscle and skin homogenate from rat, rabbit and pig and in skin homogenate from man. Within the same species there was no difference in the enzymatic activity in whole blood, serum and plasma. Comparing the enzymatic activity in blood fractions from the various species, the activity was higher in man followed by rabbit, rat and pig, respectively. The enzymatic activity in the tissue homogenates was general highest in liver followed by kidney, brain, buccal mucosa, muscle and skin. The tissue homogenate from rabbit had higher enzymatic activity than those from rat, which again showed higher activity than those from pig. Comparison of the Michaelis-Menten parameters, K(m) and V(max), obtained using pig and rat serum respectively, suggested that morphine-3-propionate has a lower affinity for enzymes present in pig serum than in rat serum and that the enzymes found in pig serum has a lower hydrolytic capacity than those in rat serum. The results obtained in this study indicate that the three animal species investigated, can serve as a model for man in bioactivation studies on morphine-3-propionate and possibly for other short chain morphine-3-esters as well.