The study was made of 64 guinea pigs with induced generalized tuberculosis which underwent no treatment, 60 infected animals receiving chemotherapy 2 weeks after the inoculation and 16 healthy animals. Citrate plasma and bronchoalveolar lavage (BAL) fluid of all the animals was examined for fibronectin (FN) concentrations using ELISA. The measurements were made 1 week, 1 and 2 months following inoculation and 2 weeks, 1.5 and 2.5 months after the start of the treatment. Histological investigations of the lungs, liver and spleen were performed at the same terms. It was established that for generalized tuberculosis developing spontaneously FN changes are characterized by multidirectional trends, seen more markedly at the terminal stage of the process. A long-term specific therapy was associated with rising FN levels in the blood and BAL fluid.