['To determine the reversibility of bone mineral density after the cessation of GnRH agonist treatment for endometriosis.', 'Longitudinal trial with 6-month treatment period and 6-month follow-up.', '28 Japanese premenopausal women with endometriosis.', 'Daily dose of 400 micrograms nafarelin was administered for 6 months.', 'The spine bone mineral density was measured by dual energy X-ray absorptiometry, and blood and urinary bone metabolic parameters were analyzed. The decrease of lumbar bone mineral density, which took place during treatment, continued during the first 3 months after the cessation of treatment and did not return to the initial baseline level even at 6 months after the withdrawal of treatment. The biochemical parameters, which showed a state of enhanced bone turnover during nafarelin treatment, almost returned to the pretreatment level 6 months after the termination of treatment.'] Is reduction of bone mineral density by gonadotropin-releasing hormone agonist , nafarelin , completely reversible at 6 months after the cessation of administration?