Seventeen patients were studied to test the hypothesis that a large evening meal influences the fasting glucose level and glucose tolerance the following morning in patients with type 2 diabetes. Oral hypoglycemic agents were discontinued for 2 weeks. The baseline fasting plasma glucose levels were 12.3 +/- 0.9 mmol/L. Fasting and postprandial (post-Sustacal) glucose, insulin, and C-peptide measurements were performed the morning after the patients received three separate meal protocols spaced 1 week apart. The caloric distribution of the meal protocols was (1) 7 kcal/kg of ideal body weight breakfast and lunch and 14 kcal/kg supper (small supper); (2) 7 kcal/kg breakfast and lunch and 28 kcal/kg for supper (large supper); and (3) 14 kcal/kg breakfast and lunch (no supper). Fasting glucose level were higher the morning after the large supper compared to no supper (13.6 +/- 0.7 versus 12.3 +/- 0.5 mmol/L, p < 0.05) and also to the small supper (13.6 +/- 0.7 versus 12.5 +/- 0.6 mmol/L, p = 0.05). No difference was observed in the fasting glucose levels between the small supper and no supper (p > 0.2). The fasting insulin and C-peptide levels, and the post-Sustacal areas under the curve of glucose, insulin, and C-peptide did not differ among the meals. In patients with type 2 diabetes, a large evening meal is associated with a modest elevation in fasting glucose the following morning.