Age-related changes in motor endplates were studied in the fibularis longus, semitendinosus and longissimus muscles in pigs. They develop from small, compact AChE-active figures in fetuses to typical myoneuronal synapses with a branched subsynaptical structure of AChE-active units. High correlations were found between size of endplates and both myofibre diameter and body mass. Growth analyses with respect to age, as well as allometrical approaches, showed that endplate growth slightly precedes that of myofibres, with both having similar growth patterns. The morphological changes, however, imply that the increment of synaptical area could lag behind that of myofibres.