The usefulness of glycosylated hemoglobin as a prenatal screening test for carbohydrate intolerance was studied in 806 consecutive subjects by correlating glycosylated hemoglobin to 1-hour post-50 gm Glucola plasma glucose (1 degree G) levels, and 3-hour oral glucose tolerance tests (3 degrees GTT). Sixty-seven subjects whose 1 degree G greater than or equal to 150 mg/100 ml received a 3 degrees GTT; 12 were diagnostic of carbohydrate intolerance. Compared to carbohydrate-tolerant controls, carbohydrate-intolerant gravid patients had higher 1 degree G (p less than 0.001) and glycosylated hemoglobin (p less than 0.05) levels. Linear regression analysis of 1 degree G and glycosylated hemoglobin demonstrated r = 0.35 (p less than 0.0001). Compared to the glycosylated hemoglobin test, the 1 degree G screening test has greater specificity, sensitivity, and predictive value for a positive diagnosis. Consequently, the 1 degree G is a better routine screening test for carbohydrate intolerance than is glycosylated hemoglobin.