A morphine-like spasmolytic action (not naloxone reversible; involving the inhibition of acetylcholine release) and also effects on the transmural transport of electrolytes (Na+ and K+) and water have been reported as possible modes of the antidiarrhoeal action of polar fractions of Psidium guajava leaf extractives. Fresh leaves of Psidium guajava collected from the vicinity of the campus of the Universiti Sains Malaysia, Kelantan State of Malaysia, were washed in water and air-dried at a room temperature of 22 0C. The material was then oven-dried at 60 0C for 3 days, machine-ground into a coarse powder, and extracted with methanol (75%) for a total of 48 hours. The extract was centrifuged for 15 min. at 2,000 rev/min, and the supernatant was dried by rotary evaporation. A stock solution of 200 mg/ml in sterile distilled and deionised water was prepared, and the pH was adjusted to 7.2 with 0.01N HCl.The objective for this study was to verify if the reported modes of the antidiarrhoeal action should be broadened to include direct antimicrobial actions on some of the more common bacteria known to cause toxin-induced acute diarrhoea. Serial dilutions of a watersoluble, freeze-dried methanolic extract were tested on 10 such organisms, grown separately on nutrient agar plates, to determine the minimum inhibitory concentration (MIC) for each of these bacteria. These included the causative agents for (i) enteric fever (Salmonella typhi, Salmonella paratyphi A, Salmonella paratyphi B and Salmonella paratyphi C), (ii) food poisoning (Salmonella typhimurium and Staphylococcus aureus), (iii) dysentery (Shigella dysenteriae, Shigella flexneri and Shigella sonnei), and (iv) cholera (Vibrio cholerae). The growth of all these organisms was inhibited at the MIC of 10mg/ml of the extract, which is equivalent to 2.5Âµg/ml of active extractable flavonoids . The most sensitive organisms (MIC = 1mg/ml) were Staphylococcus aureus, Vibrio cholerae and Shigella flexneri.