Ninety-eight patients with different patterns of chronic nonspecific pulmonary diseases (CNPD) were examined for thymus-dependent immunity. The clinical manifestations of T lymphocyte dysfunction included a torpid recurrent inflammatory process in the respiratory system, respiratory viral infections, short-term efficacy of antibacterial drugs. The patients demonstrated a decrease in the number of T lymphocytes, in production of immune interferon, and in secretion of serum thymic humoral factor. Application of tactivin, a new immunomodulator, is an effective approach to correction of the disorders enumerated. The drug has a beneficial effect on inflammatory process, reduces the symptoms of virus-induced intoxication. Administration of repeated tactivin treatment made it possible to shorten the time of repeated tactivin treatment made it possible to shorten the time of staying at hospital, to reduce the frequency of CNPD relapses from 80 to 36% within the period from 2 months to 1.5 years. This permits recommending the drug during resistance to antibiotic therapy.