We have constructed a five-compartment model of insulin kinetics. The model structure was chosen to reflect insulin distribution in systemic plasma, hepatic plasma, and interstitial fluid and insulin binding to the liver and peripheral receptors, and it included receptor-mediated and non-receptor-mediated insulin degradation. Model parameters were estimated from plasma insulin concentrations measured during hyperinsulinemic euglycemic clamp studies. In the fasting condition, the model-derived mean residence time of endogenously secreted insulin was 71 min, of which 62 min were spent bound to the liver receptor, 6 min bound to the peripheral receptor, 2 min circulating in hepatic or systemic plasma, and 1 min in the interstitial fluid. More than 80% of total insulin was bound to the liver receptor, indicating that the liver is by far the largest insulin reservoir. The model was employed to assess the effect of chloroquine on insulin kinetics in patients with non-insulin-dependent diabetes mellitus (NIDDM). Chloroquine significantly altered parameter vector. However, the mean residence times of insulin in the system and in the periphery were not affected, indicating that the beneficial effect of chloroquine in patients with NIDDM under conditions of euglycemia could not be attributed to changes in insulin kinetics.