Background and Objectives: In countries with a high frequency of tuberculosis, there are problems not only with active lung tuberculosis but also with past lung tuberculosis. Cases with sequel tuberculosis very frequently present with complaints like tuberculosis, and it is very hard to determine whether it is a sequel tuberculosis complication or reactivation of tuberculosis. In this study, we measured the serum reactive oxygen metabolite ( ROM) levels of patients with active pulmonary tuberculosis and healthy controls, and investigated if these metabolites can be used as a criterion for differentiation between active pulmonary tuberculosis and sequel pulmonary tuberculosis. Methods: 40 patients with active tuberculosis, 35 patients with sequel pulmonary tuberculosis and 30 healthy control subjects with a similar age range and sex distribution were included in the study. Serum total ROM levels were detected in the patients and control group. Results: Mean serum ROM values were 994 +/- 236, 551 +/- 135 and 236 +/- 59 U/l among active lung tuberculosis cases, sequel lung tuberculosis cases and the healthy control group, respectively. As a result of these findings, serum ROM levels of active lung tuberculosis cases and sequel lung tuberculosis cases were significantly higher than those of the control group ( both p < 0.001). The serum ROM levels of active lung tuberculosis cases were also significantly higher than those of sequel lung tuberculosis cases ( p < 0.001). Conclusions: In the light of our findings, it may be assumed that serum total ROM values can be used as an activity criterion in the differentiation of active lung tuberculosis and sequel lung tuberculosis. Copyright (C) 2005 S. Karger AG, Basel.