The effect of oestriol (3 mg for 3 mth), oestradiol valerate (2 mg for 3 mth) and ethinyloestradiol (0.025 mg for 21 days) on sex hormone binding globulin (SHBG), transcortin, ceruloplasmin and pregnancy-associated macro-globulin (PAG) was analysed in oestrogen-deficient women. The doses of oestrogens were therapeutically effective for the treatment of oestrogen-deficiency symptoms. Treatment with 0.025 mg ethinyloestradiol induced a 281% increase in PAG, a 119% increase in SHBG, a 74% increase in transcortin and a 74% increase in ceruloplasmin levels. Administration of 2 mg oestradiol valerate resulted in a 40% increase in SHBG, a small increase in transcortin and ceruloplasmin, whereas PAG levels remained unaffected. None of the parameters tested were affected by oestriol treatment. PAG was clearly the most sensitive parameter for ethinyloestradiol while SHBG was the most sensitive parameter for oestradiol valerate. These results show no relationship between clinical efficacy and effect of plasma protein synthesis, and demonstrate that one has to be very careful when comparing potency estimates for different oestrogens and different parameters.