A longitudinal study was carried out in 40 patients with typhoid fever, 21 with infectious hepatitis and 15 with amebic liver abscess in order to determine percentual values of lymphocytes T and B in relation with age and nutritional state as compared to a normal control group. In patients with typhoid fever, a decrease of percentual values of lymphocytes T was observed starting on the second week of evolution with intensification on the third week, predominating in patients less than seven years of age and in malnourished cases (p less than 0.001) and late recovery in the group of patients less than seven years old. In patients with acute infectious hepatitis, there was depression of lymphocytes T that persisted to the eighth week and was independent of age, but more severe in the malnourished (p less than 0.001). In cases with amebic liver abscess, depression of lymphocytes T was observed during the first six weeks of evolution without relation with age or the state of nutrition, but with increased slowliness in recovery in patients under seven years. There were no disturbances in lymphocytes B nor in cutaneous response to dinitrofluorobencene (DNFB) in the three groups of patients.