To estimate the weight deficit and body composition of cases of pulmonary TB (PTB), and assess the roles of HIV and the acute-phase response, a cross-sectional study was carried out in Tanzania. Weight, body mass index (BMI), arm muscle area (AMA), arm fat area (AFA) and the serum concentration of the acute-phase protein alpha(1)-antichymotrypsin (serum ACT) were evaluated for each of 532 cases of PTB and 150 'non-TB' controls. On average, the female cases of PTB not only weighed 7.8 kg less but also had BMI that were 3.1-kg/m(2) lower, AMA that were 14.8-cm(2) lower, and AFA that were 7.6-cm(2) lower than those seen in the female subjects without TB. Similarly, on average, the male cases of PTB weighed 7.1 kg less and had BMI that were 2.5-kg/m(2) lower, AMA that were 18.8-cm(2) lower and AFA that were 1.6-cm(2) lower than those seen in the male subjects without TB. Although HIV infection was associated with a 1.7-kg lower weight and a 0.6-kg/m(2) lower BMI (with deficits in both AMA and AFA) among males, it was not associated with any such deficits among the female subjects. Elevated serum ACT was found to be a negative predictor of BMI, AMA and AFA, partially explaining the effects of the PTB but not those of the HIV. There is need for a better understanding of the determinants and effects of loss of fat and lean body mass in HIV-positive tuberculosis.