Seventy five cases (50 males, 25 females; mean age 20.2 +/- 5.8 years), whose stools were positive for cysts and/or trophozoites of Giardia lamblia, were studied for their clinical profile and therapeutic response to metronidazole and tinidazole. Maximum frequency of cases (41.2%) was noted upto 20 years of age, and it declined with advancing age. A majority of them (41.3%) presented with non-specific symptoms while 38.6% were asymptomatic parasite carriers. Features of malabsorption were observed in 12% of cases and 8% presented with acute illness, having explosive, watery, foul smelling diarrhoea along with crampy upper abdominal discomfort. Most of them (62.5%) had blood group A. Tinidazole (97.5%) was more efficacious (P less than 0.01) than metronidazole (54%) in a single dose of 50 mg/Kg, with good tolerance. Tinidazole can be recommended for the treatment of giardiasis in individual cases as well as in families and close communities.