To serve the government policy on the development of drug from medicinal plants, the medicinal plant researches are promoted. Hopefully, the findings will be implemented in the primary health care and lead to the development of new medicinal plant drugs Guava, one of the potential medicinal plants recommended for primary health care is selected for these studies. An in vivo anticough effect of guava, Psidium guajava, Linn. was evaluated in white Wistar rats and guinea pigs. The animals were divided into 6 groups of each 10 animals. Group 1,2 were served as control and normal saline(NSS)-treated group

group 3-6 were injected intraperitoneally with dextromethorphan and 1, 2, 5 g/kg BW of Iyophilized fresh guava leaves juice respectively. Induction of coughing in the experimental animals were made by mechanical stimulation of the tracheal bifurcation of slightly anestihetized animals, and chemical stimulation using capsaicin aerosol. Mechanical stimulation showed inconsistent results. Therefore this model is unsuitable for evaluating anticough activity. However, the doses of 1, 5 g/kg BW of guava could decrease the frequency of cough compared to the control in male rats. Chemical stimulation with capsaicin produced cough in both animal specis. Histopathological examination of trachea showed no obvious inflammation, which indicated that cough is resulted from irritating effect rather than inflammation. The dose of 2, 5 g/kg BW of guava could decrease the frequency of cough significantly from control (P