Peptides and proteins have received much attention in recent years as candidate drugs. Vapreotide (RC-160) is a somatostatin analogue used for the therapy of hormone-dependent tumors and endocrine disorders. Like other peptides, it cannot be administered by the oral route and its plasma half-life is relatively short after parenteral administration. For these reasons, its use would be greatly enhanced by a sustained delivery system capable of maintaining controlled plasma levels of the peptide over an extended period of time. Poly(d,l-lactide-co-glyco (PLGA) are biocompatible biodegradable materials useful for a variety of applications, including the design of controlled-release systems for pharmaceutical agents. RC-160 pamoate loaded implants are proposed in this work as a means for controlling the drug release. Various PLGA were studied as biodegradable drug carriers and their in vivo release profiles were examined. Poly(d,l-lactide-co-glycolide) implants containing RC-160 were prepared by an extrusion method and the drug release was evaluated in vivo in rats using a radioimmunoassay method. The effects on the release profile, obtained by varying molecular weight, lactide/glycolide ratio and core loading were studied. The effects of polymer end groups were also investigated. Gel permeation chromatography was employed to characterize the loss in molecular weight of the different polymers after extrusion and γ-sterilization. It was found that drug loading, polymer molecular weight, copolymer composition and end group modifications were critical factors affecting the in vivo release properties. However, even though complex problems still exist, controlled release of peptides from biodegradable PLGA matrices can be achieved.