Immunological events, not the bacilli, are responsible from the tissue damage of tuberculosis. Clarifying the immunological events may lead to the development of new approaches to treatment and defence against tuberculosis disease. In this study we aimed to determine the serum levels of interleukin-2 (IL-2) and C-reactive protein (CRP) in patients with tuberculosis and evaluate the relationship with clinical and radiological findings. The study included 60 patients (mean age: 37 +/- 12 years, all male) with newly diagnosed pulmonary tuberculosis and 23 healthy controls (mean age: 40 +/- 13 years, all male). Admission symptoms, clinical features, demographic data, laboratory investigations and radiological findings were all recorded into the study form. Serum samples which were obtained for determination of IL-2 and CRP levels were preserved at -80 degrees C. While serum IL-2 levels were similar in patients with tuberculosis and healthy controls, serum CRP levels were significantly higher in patients with tuberculosis (p< 0.001). There was a positive correlation between serum IL-2 level and the diameter of cavity (p= 0.012). CRP levels were significantly higher in patients who admitted with fever (p= 0.001) and weight loss (p= 0.024). Serum CRP levels were significantly higher in patients who had involvement of four or more zones (p= 0.029) and multiple cavitary disease (p= 0.001). There was a positive correlation between serum CRP level and the diameter of cavity (p= 0.004). In conclusion, apart from the diameter of cavity, serum IL-2 levels were not correlated with any clinical, laboratory or radiological parameter. Serum CRP levels were a good indicator of disease severity.