This study was undertaken to evaluate whether the presence of thyroid antibodies in euthyroid women is associated with an adverse outcome in an in-vitro fertilization (IVF)-embryo transfer programme. In 24 women (study group: mean age +/- SD: 31.5 +/- 4.4 years) who failed to conceive after having three or more cycles of IVF and embryo transfer, serum concentrations of thyroglobulin (TG), thyroid peroxidase antibodies (TPO) and anticardiolipin antibodies (IgG and IgM) were measured using commercially available kits. The control group comprised 24 consecutive patients without endocrine dysfunction (mean age +/- SD: 30.3 +/- 4.1 years) seeking infertility treatment in our department of assisted reproduction. All patients in both the study and the control groups were determined to be euthyroid by demonstrating normal concentrations of thyroid-stimulating hormone (TSH). In the study and control groups respectively, 13 and two patients demonstrated positive titres of TG, TPO or both thyroid antibodies (Fisher's exact test: P = 0.002). Mean serum concentrations of TG were significantly increased in the study group compared to the control subjects (156 +/- 167 IU/ml versus 33.5 +/- 32.0 IU/ml; U-test: P = 0.009). Serum concentrations of TPO and anticardiolipin antibodies were similar in both groups. Our investigations revealed that thyroid antibodies might be independent markers for reproductive failure in an IVF-embryo transfer programme.