The objective of the study was to assess the possible differences in effects of Implanon and Norplant implants on carbohydrate metabolism. This is a 2-year open randomized study of 80 implant (Implanon and Norplant) acceptors. Oral glucose tolerance test (OGTT) was performed before implant insertion and at 6, 12, and 24 months after implant insertion. Glycosylated hemoglobin A(1)C was measured in fasting samples and plasma samples during OGTT were tested for glucose and insulin levels. There was a significant increase in the area under the curve for both glucose and insulin during OGTT within each group with increasing duration of use. However, there was no significant change in the fasting plasma glucose values. There was no significant difference in the carbohydrate parameters between the two groups during implant use, except for a minimal but statistically significant rise in fasting glycosylated hemoglobin A(1)C levels at 24 months in the Implanon group. Both implants appear to induce mild insulin resistance but no significant change in serum glucose levels. These alterations in carbohydrate metabolism should have no clinical significance in healthy women.