Prolonged oxygen therapy (POT) was administered in addition to basic one in combined treatment of 47 patients with chronic obstructive bronchitis, secondary pulmonary emphysema, diffuse pneumosclerosis, chronic pulmonary insufficiency grade 1 and 2. The patients recieved 38 % oxygen for 15 hours per day during 30 days. Having thoroughly analysed the results of treatment and literary data, the authors suggest their own algorithm of indications for POT. The algorithm is based, aside from initial pa02 , on the value of pulmonary physiological shunt, which is an objective and integral parameter in the authors ’ opinion, and its change pattern under the influence of increased oxygen concentrations. The algorithm contains recommendations aimed at reducing the risk of possible respiratory disorders due to the cessation of hypoxemic stimulation in patients with hypercapnia associated with marked hypoxemia.