Based on an analysis of the results of the use of mesomorphic thermography, the authors have worked out thermographic criteria for differential diagnosis of pulmonary diseases. Altogether 100 patients with acute pneumonia, 17 with exacerbation of chronic pneumonia, 47 with acute bronchitis and 63 with exacerbation of chronic bronchitis were examined. In acute pneumonia and chronic pneumonia exacerbation, foci of hyperthermia appeared in the projection of a focus of infiltration. The intensity of the foci of hyperthermia was found to depend on the inflammatory process spreading. In acute bronchitis and chronic bronchitis exacerbation, the zones of hyperthermia were localized in the projection of the lung root to the posterior surface of the chest or along the spine with a potential enlargement upwards. Thermosymmetry with a temperature gradient not exceeding 0.6 degrees C may be regarded as thermographic criterion for the patients' recovery.