This study was designed to investigate the behavior of serum glucose and insulin in response to an oral glucose load in chagasic patients with the indeterminate clinical form of the disease. Sixteen chagasic patients and 28 healthy control subjects were studied after an overnight fast and during 2 h after ingestion of 100 g glucose. There were no significant differences in serum glucose levels before and 2 h after the glucose load between chagasic and control subjects. However, in 8 chagasic patients, the total area under the insulin curve was significantly lower (2976 +/- 448 microU ml-1 120 min-1) than in the control (10123 +/- 995 microU ml-1 120 min-1) and in the remaining chagasic patients (9220 +/- 826 microU ml-1 120 min-1). These results suggest that the hypoinsulinemia of this subgroup of chagasic patients may be secondary to reduced insulin secretion and/or to increased peripheral insulin sensitivity probably related to autonomic dysfunction.