Carbohydrate metabolism was prospectively studied in 28 women using triphasic oral contraceptives (TOC) for two years. They were tested using a 100-gram oral glucose tolerance test with measurements of plasma glucose and insulin levels during the three-hour test. The women were randomly assigned to either a norethindrone-containing TOC or a levonorgestrel-containing TOC. Both types of drugs contained the estrogen ethinyl estradiol. No significant changes were noted in the norethindrone TOC group. The levonorgestrel TOC two-year test had a significant elevation of the 0.5- and 2-hour plasma glucose values and the fasting insulin value. These data show that the two triphasic oral contraceptive preparations affect carbohydrate metabolism differently.