During a 30-month period, changes in carbohydrate metabolism (measured by oral glucose tolerance test) were studied in 20 Norplant acceptors. Changes were first observed one month after Norplant insertion and peaked between 12-18 months. The area under the glucose curve rose by 12.3% and 40.5% one and 12 months post insertion, respectively. At 18, 24 and 30 months the rise was, respectively, 41.9%, 40% and 38.6%. Although the changes under the insulin curves were similar, the increase at one month was doubled (25.7%). Only fasting insulin values showed very slight and insignificant changes during the 30-month period. All the changes were, however, within the normal limits for healthy women. We conclude that although Norplant induces changes in carbohydrate metabolism, these changes remain within normal limits, peak at 12 months and either remain the same or decrease with time.