The oral glucose tolerance test (OGTT) has been the recommended method of screening for the diagnosis of gestational diabetes. Based on the glycemic index of common foods, a standard meal was designed as a substitute meal test (SMT). It consisted of 3 slices of toast (75 g) with 60 g of jam, 11 g of sugar in a cup of tea, and 150 g of canned puree sweetened with sugar (8%), for a total of 118 g of available carbohydrate and a total of 518 cal. Plasma glucose concentrations of 46 pregnant women in the 2nd and 3rd trimesters were determined at 20 minute intervals for 3 hours after ingestion of this SMT, and were compared with those after a 100 g OGTT meal. There was a high correlation (r = 0.96, p less than 0.001) between comparable glucose concentrations after the 2 tests. With the SMT there were significantly fewer side-effects (nausea and vomiting), a higher level on preference scoring and reduced interassay variability of glucose levels after 2 hours. 6 gestational diabetics were diagnosed by the OGTT. In these patients glucose concentrations were higher than 3 standard deviations above the mean 2 hours after ingestion of the SMT. We propose the SMT as a side-effect-free, reliable and convenient alternative to the OGTT in pregnancy.