The investigation was carried out in 125 patients with pulmonary tuberculosis in different stages of evolution. The treatment was that granted, used in triple and/or quadruple scheme twice a week. In the greatest part of the patients the concentration of serum fibronectine (sFN) was followed in its dynamics. A reasonable increase (statistical average) of the sFN was found in the patients with tuberculosis (tbc), active at the first treatment. The values regressed slowly, parallel to the favourable evolution under treatment. In the chronic forms, values situated at the normal or at the inferior limit were recorded. They were probably due to the sum of factors often met in these patients: protein-caloric malnutrition, chronic alcoholism with afferent hepatopathies, nonspecific chronic bronchial suppurations. No significant correlation of the sFN concentration was noticed in relation to the radiologic extension of the lesions, to the structure of the chemotherapeutic regimen, or to age. There exists a large variability of the sFN concentration in tbc, both at the beginning and during chemotherapy. The sFN level is not enough for the assessment of the disease stage or evolution; for increasing its informational value, the concentration of the immune circulatory complexes (ICC) and the lymphocytic subsets T were investigated.