Biopsies of M. gastrocnemius and Nervus suralis of 12 patients with advanced disturbances of circulation were examined by means of morphometrical and histochemical methods. The histological picture of a neurogenic atrophy of the muscle fibres with partially strong hypertrophy of the slow-twitch fibres was found. The main reaction patterns and the pathogenetic mechanisms are discussed. Alterations in the ratio of type I and type II fibres are described. Fiber type disproportions, i.e. more than 75% type I fibres, may suggest that in hypoxia the type II fibres are more intensely damaged than type I fibres. There are correlations between pathological fibre distribution and the success of vasosurgical treatment.