We initially investigated the effects of a gonadotropin-releasing hormone analog, leuprolide acetate, in 28 patients with moderate to severe functional bowel disease in a phase-II, randomized, double-blind, and placebo-controlled study using Lupron Depot 3.75 mg (which delivers a continuous low dose of drug for one month) or placebo given intramuscularly. After completing that 12-week study period during which their symptoms had improved significantly (P < 0.01-0.5), the 28 patients were allowed to continue receiving leuprolide acetate; they were monitored for an additional 40 weeks. Of those 28, 25 (89%) finished the 52-week treatment. Drug administration was changed from the monthly low-dose form of leuprolide acetate to a daily subcutaneous dose that was gradually increased from 0.5 mg daily to an effective therapeutic dose (1.0-1.5 mg). All subjects received estrogen replacement during this period. Continued use of leuprolide acetate at maximum therapeutic dosage and over longer periods of time produced even more striking and significant changes in the disabling and debilitating symptoms of functional bowel disease. Nausea, abdominal pain, early satiety, anorexia, and abdominal distension decreased markedly (P < 0.0001) and vomiting was also reduced (P < 0.01) more than in the short-term, low-dosage, double-blind study. Combined total symptom scores and overall assessment also changed significantly in the long-term phase (both P < 0.0001).