Fifty-four intravenous glucose tolerance tests were performed in 12 normal individuals and 21 thermally injured patients. In the 17 hypermetabolic burn patients studied between the 6th and 16th days postinjury, fasting blood glucose was elevated (111 +/- 7 mg/100 ml, mean +/- SE compared to 85 +/- 3 in controls, P less than 0.001), but the instantaneous proportionality constant for glucose disappearance (k) was similar to that obtained in normal individuals (5.27 +/- 0.51, 100/min vs 4.01 +/- 0.58 in normals, NS). Fasting serum insulin concentrations were comparable in the 12 normals and 17 hypermetabolic burn patients (22 +/- 3muU/ml in normals vs 22 +/- 2), as was fasting insulin corrected for fasting glucose (24 +/- 3 in normals vs 21 +/- 3, NS), initial insulin response (0-10 min delta insulin, 58 +/- 13 in normals vs 67 +/- 10, NS) or total insulin response corrected per unit glycemic stimulus (insulinogenic index, 0.48 +/- 0.10 in normals vs 0.52 +/- 0.07, NS). With time following injury, the proportionality constant for glucose disappearance and insulin response decreased, and these alterations were related to the posttraumatic weight loss. In the 5 convalescent patients studied between the 37th and 90th days postinjury, glucose and insulin dynamics appeared similar to those observed in starved man. In these burn patients, hypermetabolism and negative nitrogen balance occurred in association with a normal insulin response to glucose. Increased hepatic gluconeogenesis appears to be characteristic of the catabolic response to this stress, directed by increased glucagon and catecholamines, not a decrease in fasting insulin or dampened insulin response.