The aim of the study was to evaluate the functional state of the hypothalamo-pituitary-gonadal axis and to assess the concentrations of MPA in the peripheral blood during very long-term use of depo-medroxyprogesterone acetate (DMPA) as a contraceptive agent. The concentrations of MPA, sex-hormone binding globulin (SHBG) and the different pituitary and gonadal hormones in the peripheral blood were measured in nine 26-41 year old women. They had for 4.4-10.6 years (mean 8.9 years) been receiving DMPA im in a dose of 150 mg every 12th week as a contraceptive. Blood samples were obtained immediately before an injection of DMPA, 2 weeks later, and again immediately before the next injection. SHBG was measured by radio-electro-immunoassay; MPA, gonadal and pituitary hormones by RIA. The investigation showed that the oestradiol levels - even after very long-term use of DMPA - were still within the normal range for the early follicular phase. Gonadotrophins and prolactin were within the normal range for eumenorrhoeic women as well as the concentration of SHBG. MPA did not accumulate in the plasma. The changes in the plasma levels of oestradiol, MPA and SHBG after each injection disappeared within 12 weeks. The study appearts to warrant the conclusion that even up to 10 years' use of DMPA in a dose of 150 mg im every 12th week as a contraceptive agent, does not induce hormonal changes different from those seen after the very first injection.