Alloxan reduced whole pancreatic blood flow by 50%, but almost doubled islet blood flow. Glucose did not affect whole pancreatic blood flow, but increased islet blood flow 100%. Approximately 10% of the islets in control and glucose-injected rats contained microspheres, compared with about 25% in alloxan-injected rats (P < 0.001). When the islets containing a certain number of microspheres were compared, alloxan induced a homogeneous shift of the curve to the right, i.e., increased the number of islets that contained all amounts of microspheres. Glucose preferentially increased only the fraction of islets containing > or = 3 microspheres.