Abstract 1. 1. Muscle fibre types were identified histochemically by their actomyosin ATPase and SDH activities. 2. 2. Several myosin isoforms and a distict type of myosin heavy chain (MHC) were detected in red and white skeletal muscles as revealed by pyrophosphate and SDS gel electrophoreses. 3. 3 Results of an electrophoretic analysis of myosins are discussed in the light of their histochemical and functional properties.