A survey on the nutritional status and cell-mediated immune function of 47 hospitalized patients with active pulmonary tuberculosis and healthy controls was conducted. In the patients group: 1) Anthropometric measurements, such as %ideal body weight (%IBW), %arm circumference (%AC), %arm muscle circumference (%AMC) and %triceps skin fold (%TSF), were significantly reduced. 2) Visceral proteins including serum albumin (Alb), transferrin (Tf), prealbumin (PA) and retinol binding protein (RBP) were significantly reduced. 3) The imbalance of plasma amino acids, which was characterized by the depression of Fischer ratio, a molar ratio of branched chain amino acids (BCAA) to aromatic amino acids (AAA), was observed. Fischer ratio was significantly correlated with anthropometric measurements (%IBW, %AC and %AMC). Delayed-type hypersensitivity to DNCB (2,4-dinitrochlorobenzene) and lymphocyte transformation to phytohemagglutinin (PHA) and concanavalin A (Con A) were significantly impaired in the patients group, whereas NK cell activity was higher than that of controls. Alb, PA, RBP and Fischer ratio were significantly lower in the patients with reduced DNCB reaction than in those with normal responses. Lymphocyte transformation was significantly correlated with Fischer ratio, and NK cell activity was significantly correlated with Alb, PA, RBP. These data may suggest that the imbalance of plasma amino acids represented by the reduction of Fischer ratio and the depletion of visceral proteins are closely related to the impairment of lymphocyte function in the patients with active pulmonary tuberculosis.