OBJECTIVES: Though the greatest proportion of irritable bowel syndrome (IBS) patients report a mixed bowel pattern (IBS-Mixed), no available therapies have been rigorously evaluated in this subgroup. This study aimed to evaluate the efficacy and safety of the 5-HT(4) agonist tegaserod in women with IBS-Mixed and IBS with constipation (IBS-C). METHODS: This prospective, double-blind, randomized, placebo-controlled, multicenter study was conducted in 100 centers in North America, South America, and Europe. Women with IBS-Mixed or IBS-C received tegaserod 6 mg or placebo twice daily. The primary efficacy variable was the patient's assessment of satisfactory relief over the 4-wk treatment period. The proportion of patients reporting satisfactory relief for >/=3 of 4 treatment weeks (75% rule) and individual IBS symptoms were assessed. RESULTS: In total, 661 women were randomized (IBS-Mixed 324, IBS-C 337). Baseline symptom assessments identified clear differences between the two cohorts. Tegaserod provided significant improvement in satisfactory relief of IBS symptoms over 4 wk (OR 1.75, 95% CI 1.35-2.25, P < 0.001) in both IBS-Mixed and IBS-C patients. Using the 75% rule, 52.3% of tegaserod-receiving IBS-M patients and 43.3% of IBS-C patients were responders (vs 36.3, OR 1.88, 95% CI 1.16-3.04, P < 0.010; and 28.9, OR 1.90, 95% CI 1.19-3.05, P < 0.008 for placebo, respectively). The most frequent adverse events leading to study discontinuation in tegaserod-treated patients were diarrhea (1.5%) and abdominal pain (0.9%). Overall 7% of IBS-C patients reported diarrhea compared to 12% of IBS-Mixed (placebo 2.4%, 1.8%, respectively). CONCLUSIONS: Tegaserod is effective in treating overall IBS symptoms in patients with IBS-Mixed and IBS-C.