We have studied the effects of oral contraceptives on three glycoproteins, alpha-1-antitrypsin (A1AT), gamma-glutamyltransferase (GGT) and alkaline phosphatase (AP), in terms of age (20--40 years), duration of administration, and levels of estrogens. We have confirmed that oral contraceptives increase the concentration of A1AT and the activity of GGT and decrease the activity of AP, but that the modifications are less pronounced with pills containing low levels of estrogens for GGT and AP. We observed a decrease in A1AT and GGT after 2 and 5 years of treatment, respectively, but an increase in AP. Patient age seemed to have little influence on the change in AP activity and A1AT concentration but GGT activity was higher for the 25--30 year group.