Murine carrier erythrocytes, prepared by hypotonic dialysis, were employed in the encapsulation of several compounds including [14C]sucrose, [3H]inulin, and bovine thiosulfate:cyanide sulfurtransferase (rhodanese), a mitochondrial enzyme which converts cyanide to thiocyanate. Approximately 30% of the added [14C]sucrose, [3H]inulin, and rhodanese was encapsulated by predialyzed erythrocytes, and a decrease in the mean corpuscular volume and mean corpuscular hemoglobin was observed. In the encapsulation of rhodanese a recovery of 95% of the erythrocytes was achieved and an 85% equilibrium was established. The addition of potassium cyanide (50 mM) to intact, rhodanese-loaded erythrocytes containing sodium thiosulfate resulted in its metabolism to thiocyanate. These results establish the potential use of erythrocytes as biodegradable drug carrier in drug antagonism.