The presence of nitric oxide (NO) and its role as a factor in host defence against intracellular pathogens in human macrophages is controversial. We measured the metabolites of NO (nitrite (NO2-) and nitrate (NO3-)) in urine from Ethiopian patients suffering from tuberculosis. The urinary level of NO2-/NO3- in a group of healthy Ethiopians was 1020+/-471 microM (n = 22). Untreated HIV negative patients with active pulmonary tuberculosis (1574+/-588 microM, p<0.01, n = 12) and household contacts to tuberculosis patients (1949+/-812 microM, p = 0.006, n = 7) had significantly higher levels of urinary NO2-/NO3- than the control group. Untreated HIV positive patients with pulmonary tuberculosis did not have increased levels of urinary NO2-/NO3- (1101+/-614 microM, n = 6). Some of the HIV negative untreated patients with pulmonary tuberculosis (1710+/-519 microM, n = 6) were followed up after treatment and showed a reduction in the levels of urinary NO2-/NO3- 1 week after treatment (945+/-599 microM, p<0.05). We conclude that HIV negative patients with active pulmonary tuberculosis have increased urinary levels of nitric oxide metabolites with a reduction following specific anti-tuberculous chemotherapy.