Content of free amino acids was altered in blood plasma and erythrocytes of patients with Becker-Kiner progressive muscular dystrophy; these alterations were more distinct in blood plasma as compared with erythrocytes. Spectra of individual free amino acids were distinctly altered both in blood plasma and erythrocytes. Development of the myodystrophia process correlated with alterations in glycogen and branched-chain amino acids content. The data obtained suggest the important functions of erythrocytes in intertissue transport of free amino acids. Similarity between the alterations, observed in progressive muscular dystrophy and in other pathological states accompanied by accelerated metabolism of proteins, suggests that these impairments are among the components in the adaptation reactions to metabolic stresses.