A system and method for the parenteral delivery of a drug in a biodegradable polymeric matrix to a warm blooded animal as a liquid with the resultant formation of a gel depot for the controlled release of the drug. The system comprises an injectable biodegradable block copolymeric drug delivery liquid having reverse thermal gelation properties. The liquid is an aqueous solution having dissolved or dispersed therein an effective amount of a drug intimately contained in a biodegradable block copolymer matrix. The copolymer has a reverse gelation temperature below the body temperature of the animal to which it is administered and is made up of (i) a hydrophobic A polymer block comprising a member selected from the group consisting of poly(.alpha.-hydroxy acids) and poly(ethylene carbonates) and (ii) a hydrophobic B polymer block comprising a polyethylene glycol. The liquid is stored below the reverse gelation temperature and is parenterally administered into the animal by intramuscular, intraperitoneal, subcutaneous or similar injection.