Kinetics of gut lymphocyte subpopulations were studied in normal and malnourished groups of mice infected with Giardia lamblia. The maximum parasite load was observed at second, third, and first week of postinfection in normal controls, moderate (8%) and severe (3%) protein deficient groups respectively. The number of G lamblia trophozoite in 3% protein deficient group was low compared with control groups. A significant increase in T cell population of intraepithelial lymphocytes and lamina propria in normal and moderate protein deficient groups was observed with the development of infection. It was less marked, however, in the severely malnourished group. Interplay of mucosal immune status with nutrition and G lamblia infection is discussed.