Out of 57 women with previous histories of gestational diabetes (GD), 23 were of normal weight postpartum and willing to participate in three studies characterizing oral glucose tolerance (OGTT), insulin responsiveness to intravenous glucose (glucose infusion test, GIT), and insulin sensitivity (somatostatin, insulin, and glucose infusion test, SIGIT). The experiments were performed 6-36 mo after cessation of breast-feeding. The control group comprised 10 healthy women with normal OGTT matched for age and weight. Among subjects with previous histories of GD, 9 had normal, 8 borderline, and 6 decreased OGTT. As a group, women with previous histories of GD have significantly decreased insulin response and insulin sensitivity. Furthermore, all 14 with borderline and decreased OGTT demonstrated a low early insulin response during GIT (5-min value below the upper border of the lower quartile of normals), whereas insulin sensitivity was normal in 6 and low in 8 (glucose values attained during SIGIT were lower or higher, respectively, than the lower border of the upper quartile of controls). The women with previous histories of GD and normal OGTT exhibited normal (n = 4) and low (n = 5) insulin responses. Three of the former subjects had low and the remaining 6 had normal insulin sensitivity. In conclusion, as many as 60% of normal-weight women with previous histories of GD had borderline or decreased OGTT 6-36 mo postpartum. This derangement could be due to impaired early insulin response, which in some subjects was combined with low insulin sensitivity. Follow-up of women with previous histories of GD might enlighten the pathogenesis of non-insulin-dependent diabetes mellitus.