The aim of this study was to examine more closely the interaction between thyroid function and pituitary--ovarian axis in infertile women. In 185 infertile women without clinical signs of thyroid dysfunction, TRH-tests (TSH basal and 30 min after 200 micrograms TRH i.v.) were performed in the early follicular phase in addition to routine hormonal checks (gonadotrophins, oestradiol, DHEAS, testosterone, prolactin). The women were classified as euthyroid (n = 74; TSH stim 5-20 mU/l), latent hyperthyroid (n = 31; TSH stim less than 5 mU/l), and preclinical hypothyroid (n = 80; TSH stim greater than 20 mU/l). From frozen serum, the following determinations were performed: TSH IRMA, laevothyroxine (T4), thyroxine binding globulin (TBG), microsomal (Mab) and thyroglobulin (Tab) antibodies. Various correlations between the thyroid parameters and the pituitary--ovarian axis were demonstrated. With increasing TBG concentrations, the interval between menses decreased. Overall and spontaneous pregnancy rates were highest in women with normal (less than 75th perc.) basal and stimulated TSH, high (greater than 75th perc.) T4 and low (less than 25th perc.) Mab. Women with normal Tab or high TBG experienced the highest delivery rate (77 versus 30%), while in women with low Tab or high Mab abortion and tubal pregnancies were most frequent. As only 25 women exhibited elevated Mab (greater than 500 U/ml) or Tab (greater than 200 U/ml) which correlated with elevated TSH and normal T4, the routine determination of thyroid antibodies was not necessary. The TRH-test, however, should be included in infertility work-up.