We investigated the plasma insulin binding patterns of 15 insulin-treated juvenile diabetics with a very low residual B-cell function. Determination of the insulin binding was performed after removal of therapeutic insulin. 125I-monoiodoinsulin was used and insulin binding was measured over a large range of insulin concentration. Insulin binding parameters were evaluated by Scatchard analysis of the binding data. Significantly elevated insulin binding was detected when the diabetic control was stable. These patients had a lower insulin requirement and low equilibirum dissociation constants of the high affinity antibodies. Furthermore, a strong negative correlation between the duration of insulin treatment and insulin binding could be demonstrated resulting from both decreasing antibody affinities and maximum binding capacities. We discuss the stabilizing effect of insulin antibodies on the metabolic character assuming that dissociating insulin-antibody complexes mimic a “basal insulin secretion” similar to pancreatic B-cells with residual functional capacity.