From the point of view of adaptation for flight in bats, we compared growth and LDH (lactate dehydrogenase) isozyme patterns in the pectoral and cardiac muscles of the Japanese Lesser horseshoe bat,Rhinolophus cornutus cornutus.In the pectoral muscles, the four LDH isozyme bands were recognized throughout life. In the embryo and newborn young the predominant isozyme was LDH‐3 and the relative amount of LDH‐1 was very low. The predominant isozyme of the infant in the flying stage was LDH‐1.Moreover, the percentage of B subunit of LDH isozymes in the pectoral muscles increased remarkably during the transition period from the flapping to flying stage. Thus, it is concluded that there is a reversal of LDH isozyme activity toward more anodal side (cardiac muscle type) during the transition period, which is regarded as an adaptation to the metabolic requirement at isozyme level of the pectoral muscles for an adult. This species has a highly manoeuvrable flight with low speed, like that of a butterfly. On the other hand, most of the activity in the cardiac muscles, even in the embryo, was concentrated in more anodal isozymes with LDH‐1 and LDH‐2, and consequently the percentage of B subunit showed a considerably higher value, which continued to increase gradually until the ad