The most effective therapy for endometriosis is a matter for debate. The aim of the present randomized study was to evaluate the efficacy of low doses of danazol on recurrence of pelvic pain in patients with moderate or severe endometriosis, who had undergone laparoscopic surgery and 6 months of gonadotrophin-releasing hormone analogue (GnRHa) therapy. After surgery, 28 patients with moderate or severe endometriosis underwent therapy for 6 months with GnRHa i. m. every 4 weeks. They were then randomized into two groups: group A (14 subjects) was treated with 100 mg/day danazol for 6 months; group B (14 subjects, control) did not receive any type of therapy. After 12 months of treatment, group A had a significantly (P < 0.01) lower pain score than group B. There was no significant difference between the groups in oestrogen concentrations, bone mineral density or side-effects. The results suggest that low-dose danazol therapy reduces recurrence of pelvic pain in patients with moderate or severe endometriosis, treated surgically, and has few or no metabolic side-effects.