Fifty-six patients with pelvic endometriosis were treated with a buserelin dosage of 200 mu g/day s.c. for 6 months. Scoring of the American Fertility Society (AFS) for endometriosis was performed by laparoscopy in all cases before and at the end of therapy. Serum CA-125 and estradiol levels were determined before the treatment, and monthly during therapy and follow-up (6 months; respectively). A slight positive correlation was found between serum CA-125 concentrations before treatment and AFS scores for adhesions only. Before treatment, serum CA-125 values also correlated slightly with total AFS scores of patients with adhesions. At the end of the 6-month therapy, no correlation was found between CA-125 concentrations and second-look AFS scores for implants and/or adhesions. Serum CA-125 and estradiol values were closely parallel to each other during and after therapy with the gonadotrophin-releasing hormone agonist buserelin. In conclusion, (1) adhesions may play a role in the elevation of serum CA-125 levels in endometriosis, and (2) a significant decrease in serum CA-125 values during the buserelin therapy may result from a rather different mechanism, such as ovarian suppression, other than the therapeutic effect of this agent.