The long-term effect of high-glucose condition on insulin binding to IM-9 cells was studied by incubating the cells in RPMI-1640 medium containing 450 mg/dl of glucose. Insulin binding began to decrease after incubation for 6 days in high-glucose-treated cells, and significantly decreased after 14 days due to the reduction of receptor affinity. The number of binding sites for insulin did not change by the treatment. Thus, high-glucose condition per se does not appear to induce the decrease of the number of insulin receptors on target cells, as observed in diabetic patients.