In 42 patients of various age (from 1 month to 14 years) with cystic fibrosis were analyzed ultra structure, level of adenylnucleotides and activity ATP-ase of erythrocytes, in order to characterize their membrane and energy metabolism. The studies revealed the changes in erythrocytes in the cases of cystic fibrosis. In the cases of broncho pulmonary form of cystic fibrosis were detected I and II row echinocytes, cone-shaped erythrocytes, also erythrocytes with reach-through hole in center. At mixed form of cystic fibrosis were detected more changes in erythrocytes than in other forms of this disease. Both cone-shaped erythrocytes were more than in other forms of cystic fibrosis. Also there were detected erythrocytes with holes (round, polygonal) in their center. The results of the study provide a more precise diagnosis, in time correction of disorders and a comprehensive assessment of multiple-modality treatment of cystic fibrosis.