Cassia alata Linn. is a medical plant. Its leaves have been claimed to be effective as a laxative. The studies done so far have shown no toxicity as a result of consuming Cassia alata Linn. leaves. The plant has been found to contain anthraquinones, presumed to be the active ingredient causing the laxative effect. The objective of the study was to test efficacy of Cassia alata Linn. leaves for treatment of constipation compared with a placebo and mist. alba in a multicenter randomized controlled trial carried out in one provincial and 5 community hospitals. Eighty adult patients admitted to 5 community hospitals and one provincial hospital with at least 72 hours of constipation were included in the study. Twenty-eight patients were in the placebo group, 28 in the mist. alba group, and 24 in Cassia alata Linn. group. Each patient was given 120 ml of fluid with caramel color, mist. alba, or Cassia alata Linn. infusion at bed time. Evaluation was performed after 24 hours whether the patient defecated or not. The characteristics of the patients among the three groups were not different. Eighteen per cent of patients in the placebo group passed stools within 24 hours, whereas, 86 and 83 per cent of patients in mist. alba and Cassia alata Linn. groups respectively, passed stools. The differences observed between placebo and mist. alba, placebo and Cassia alata Linn. were statistically highly significant, P less than 0.001 and clinically important. Minimal self-limited side effects, i.e., nausea, dyspepsia, abdominal pain and diarrhea were noted in 16-25 per cent of the patients.(ABSTRACT TRUNCATED AT 250 WORDS)