The effect of the alcoholic extract of the whole plant of Bacopa monniera (Scrophulariaceae) on morphine withdrawal was evaluated in vitro in guinea-pig ileum. After a 4 min in vitro exposure to morphine, addition of naloxone induced a strong contraction. Addition of various concentrations of the alcoholic extract of B. monniera (100-1000 microg/ml) 15 min before exposure to morphine reduced the naloxone-induced contraction in a dose-dependent manner. The results suggest that B. monniera extract may be useful in reducing the withdrawal symptoms induced by morphine.