Serum SHBG and ceruloplasmin (CP) concentrations were measured in women throughout a cycle of treatment with four oral contraceptives. In women receiving 150 micrograms levonorgestrel (LNG) daily both SHBG and CP decreased. SHBG also decreased, but CP increased, in women receiving ethynyloestradiol (EE) 30 micrograms with LNG 150 micrograms. In women taking 35 micrograms EE with either 600 micrograms or 1000 micrograms norethisterone, increases in CP were similar but SHBG increased more with the lower dose. Serum concentrations had not returned to pretreatment levels by eight days after cessation of dosing. The findings are compared with similar results for women taking 30 micrograms or 50 micrograms EE or an EE,LNG triphasic formulation. Serum concentrations of the gestagens were also measured. Increases in these concentrations when the gestagen was administered with EE to levels higher than expected from administration of the gestagen alone cannot be explained by increased binding to SHBG but are more likely to be due to changes in their metabolism. Differences in the responses of ostensibly closely related proteins of hepatic origin such as SHBG and CP to the oral contraceptives demonstrate that neither can be extrapolated to other pharmacodynamic responses.