An implantable artificial endocrine pancreas consisting of a coiled single acrylic copolymer capillary surrounded by a rat islets (1000/kg body weight) was implanted in 10 streptozotocin-alloxan diabetic dogs. About 5 h following implantation plasma glucose decreased from an initial mean value of 350 mg/dl to 150 mg/dl, and then to 100 mg/dl at 12 h. Plasma insulin increased to a mean of 39 mU/1 (range 23-83 mU/l) at 5 h in the recipient animals In addition a much improved plasma glucose disappearance rate (K = 1.9 plus or minus 0.3) with slightly delayed insulin responses was seen after intravenous glucose tolerance tests performed in 4 dogs at 7, 8, 10 and 18 h following implantation. These findings suggest that xenogeneic rat islets implanted as an artificial endocrine pancreas can improve glucose metabolism in the diabetic dog.