ABSTRACTTwo primary flight muscles of Myotis myotis were studied using mopphological and histochemical analysis. Two fast-twictch fiber types are histochemically identified in pectoralis muscles of M. myotis. These were classified as type IIa and type IIb according to glycine-calcium-formalin preincubation staining protocol for myosin ATPase. The primary flight muscles, serratus ventralis included type I, type IIa and type IIb fibers. Type I fibers were highly oxidative, as stained dark for NADH-TR. Type IIa fibers exhibited relatively weak staining properties for NADH-TR and SDH, indicating an intermediate oxidative capacity. Type IIb fibers showed low oxidative capacity, as indicated by weak reaction for NADH-TR. Key Words: Myotis myotis, skeletal muscles, ATPase, NADH-TR, SDH, histochemical tests.