Although epidemiological studies have shown that malnutrition is associated with the reactivation and development of pulmonary tuberculosis, little is known about their nutritional status. We studied comprehensive profile of their nutritional status. We also studied the effects of malnutrition on cell-mediated immunity in tuberculosis patients. Nutritional status was assessed by anthropometric measurements and biochemical examinations, and cell-mediated immunity was evaluated by delayed-type hypersensitivity (DTH) reaction, lymphocyte transformation and natural killer (NK) activity in 47 patients with active pulmonary tuberculosis and 47 healthy controls. Cytokine production including IL-2, IL-1 was also examined. Anthropometrics and visceral proteins were significantly lower in tuberculosis patients. Fischer ratio (BCAA/AAA), an index of plasma amino acids imbalance, was significantly (p less than 0.01) lower in the patients. DTH to 2, 4-dinitrochlorobenzene and lymphocytes transformation were attenuated in the patients. NK activity was reduced in patients with severe pulmonary tuberculosis. The patient subgroup with reduced DTH was more malnourished than another one with normal DTH. The Fischer ratio correlated significantly with lymphocyte transformation response and visceral proteins and BCAA correlated with NK activity. IL-2 production was remarkably reduced in the patient subgroup whose serum albumin was less than 3.5 g/dl. IL-1 production was remarkably reduced in the patient subgroup whose serum albumin was less than 2.5 g/dl. Patient subgroup whose serum albumin level was more than 2.5 g/dl and less than 3.5 g/dl, produced remarkably more IL-1 than those whose serum albumin was more than 3.5 g/dl. These results suggested that malnutrition characterized by the reduction of the Fischer ratio was associated with impairment of cell-mediated immunity and cytokine production in pulmonary tuberculosis.