Two species of blow flies (Diptera: Calliphoridae) were reared on tissues from rabbits administered different dosages of morphine. These species, Protophormia terraenovae and Calliphora vicina are among the first wave of insects colonizing a dead body. Two series of 3 rabbits were given dosages of 10, 20, and 40 mg/h of morphine over a 3 h period via ear artery perfusion. A morphine blood level plateau was attained after 1 h of perfusion. Two other rabbits were used as controls. Samples of tissues collected from rabbits using a coelioscopic technique were determined to have morphine concentrations similar to those encountered in human overdoses and were correlated with dosages of morphine administered. All samples from control rabbits were negative for morphine. Larvae and puparia of both species were regularly collected from each rabbit for toxicological analysis. Concentrations of morphine in larvae reared on rabbit carcasses containing morphine were significantly lower than concentrations found in the tissues. There was a decrease in concentration in morphine observed in transition from feeding 3rd instar larva to puparium. A correlation between larval concentration and tissue concentration was found only in feeding 3rd instar larvae.