The efficacy and safety of the peripheral kappa agonist fedotozine was evaluated in a double-blind, multicenter study involving 238 patients with the irritable bowel syndrome. After a two-week washout, patients were assigned to one of four groups to receive either placebo or fedotozine three times a day at doses of 3.5, 15, or 30 mg for six weeks. Patient assessment of mean symptom intensity indicated that the 30-mg dose of fedotozine was superior to placebo in relieving maximal daily abdominal pain (P = 0.01), mean daily pain (P = 0.007), and abdominal bloating (P = 0.02). Changes in bowel function and defecation disorders could not be evaluated reliably. According to the investigators, the highest dose of fedotozine markedly reduced overall disease severity (P = 0.003) and the pain component of the symptomatic profile (P = 0.009). Clinical and laboratory safety was very good. Fedotozine 30 mg three times a day therefore appears to be effective and safe in the treatment of the abdominal pain and bloating associated with IBS.