Intravenous glucose tolerance tests (IVGTT) were performed on 9 adults with sickle cell anemia and 15 normal controls. Blood samples were collected before and 1, 3, 5, 10, 20, 30, 40, 50, and 60 min after intravenous glucose infusion and used for glucose and C-peptide assays. The mean C-peptide concentration after glucose infusion was significantly (p less than 0.05) lower for the SCA patients as compared to the controls. No significant differences were observed in the glucose concentration of IVGTT between the two groups. These results suggest an inadequate insulin secretion by the endocrine pancreas in sickle cell anemia or an independent genetic abnormality in linkage disequilibrium with the beta s gene.