The ethanol extract (50%) of the whole plant of Amaranthus spinosus Linn. (Amaranthaceae) (ASE) significantly inhibited travel of a charcoal meal at three different doses of ASE, but when 400 mg/kg of ASE was repeated in the presence of yohimbine, intestinal propulsive inhibition decreased, while morphine reversed the activity. The percentages related to controls for the onset of diarrhea were 16.58, 83.42, and 116.18% at doses of 100, 200, and 400 mg/kg of ASE, while with morphine this value was 123.93% compared to controls. The percentage purging frequency related to controls was 41.09, 64.38, 71.23, and 86.30% at three different doses of ASE and with morphine, respectively. The inhibitions in intestinal accumulation were 8.9, 48.16, and 68.06% at doses of 100, 200, and 400 mg/kg of ASE, respectively, compared to control, while inhibition with yohimbine was 50.78%. Antidiarraheal indices of ASE were 23.55, 49.16, and 76.53 at the three different doses of ASE, while morphine had a maximum index of 88.45. Protection in ethanol- induced ulcer was 51.07, 55.91, 77.95, and 60.75%, but in aspirin-induced ulcer it was 41.33, 61.77, 80.88, and 74.66% at doses of 100, 200, and 400 mg/kg of ASE and with cimetidine, respectively. Lipid peroxidation was also associated with a concomitant decrease in ulcer index, while protection was 56.96, 63.29, 81.01, and 52.32% at three different doses of ASE and with cimetidine in cold restraint-induced ulcer. [ABSTRACT FROM AUTHOR]