The quality of colon cleansing and the tolerance of patients to the procedure are two major determinants of the quality of a colonoscopy. Many bowel-cleansing regimens are known, but there is no ideal regimen. Alverine citrate (Relaxyl, Spasmonal) is a spasmolytic agent that has been shown to affect responses of mechanoreceptors of the intestine to both mechanical and chemical stimuli. Patients who underwent colonoscopies at four centers were randomly assigned two different bowel-cleansing procedures. The bowel-cleansing methods were oral sodium phosphate (NaP) (Group I) and oral NaP plus alverine citrate (Group II). Patients were randomized into one of these regimens. The quality of colon cleansing was assessed by an endoscopist with an empirical, clinically meaningful 3-point scale. Both groups were similar with respect to age, gender, and pre- and postcolonoscopic diagnosis. In Group I, 76 patients (47 women and 29 men; aged 39.53 ± 7.87 years) and in Group II, 71 patients (41 women and 30 men; aged 39.78 ± 8.27 years) were included in the study. In Groups I and II, 37 (48.7%) and 41 (57.7%) patients had perfect bowel cleansing, respectively. The overall colon cleansing in the group with NaP plus alverine citrate was comparable with that in the NaP group. The tolerability of patients to the colonoscopy in the two groups was also similar. Based on the present data, adding oral alverine citrate to NaP does not increase either the quality of bowel cleansing or the tolerance of patients to the procedure.