AbstractThirty‐nine human skeletal muscle biopsies from 24 individuals were classified as normal, neuropathic, or myopathic muscle according to classical clinical observations and histopathological properties of the muscles. The content in myosin light chains (LC) of each muscle sample was analyzed by means of a new technique of polyacrylamide gel electrophoresis that gives an improved discrimination, involving isoelectrofocusing of the muscle homogenate for the first dimension and successive migration in a urea‐containing gel for the second dimension. Four different LC patterns have been observed in the normal muscles; these four patterns and three different ones have been observed in the pathological muscles. No apparent correlation exists between the myosin LC content and the histochemical fiber typing. It is concluded that the myosin LC are apparently not a useful marker to detect the normality or the pathology of human mus