Lippia alba (Mill.) N. E. Brown Verbenaceae, known popularly as 'Juanilama' or 'Salvia Sija', is prized widely in folk medicine in Guatemala. Its leaves are employed as an infusion and decoction as a remedy for stomach problems, dysentery, colds and cough, febrifuge, as well as a sedative and in spasmolitic remedies. The present study reports the effects of the infusion of L. alba on the rat gastric mucosa. The following behavioural parameters were evaluated: (a) gastric irritancy test in Wistar rats; (b) antiulcer activity, short term and long term; (c) acid secretion; (d) measurement of total proteins; (e) estimation of total protein bound and nonprotein sulfhydryl groups. Ranitidine (100 mg/kg, p.o.) was used as the reference antiulcer drug. Oral treatment with the infusion (12.5 g dry plant/kg) did not cause gastric irritancy in the rats treated during five consecutive days. In addition, the oral administration of L. alba was found to be effective at preventing gastric ulceration induced by indomethacin (50 mg/kg, p.o.) in rats in the short term (1 day) and long term (5 days).