A specific histochemical staining of serial cross sections of frozen muscle samples for AChE activity was performed to investigate the distribution of sarcoplasmic AChE activity and its relationship to the motor end plate in individual muscle fibers of 1-, 2-, and 6-week-old normal and dystrophic chickens. A photographic cytophotometric technique was used to determine AChE activity. There were no differences between normal and dystrophic muscle fibers in the distribution or level of AChE activity at both 1 and 2 weeks of age. By 6 weeks, AChE activity had spread to either side of the motor end plates for approximately five times the distance found in normal fibers. In addition, the level of AChE activity had almost tripled in dystrophic fibers in comparison to normal fibers. These findings suggest that dystrophic chicken muscle develops similarly to normal muscle with respect to AChE localization and level of activity for at least 2 weeks following hatching, and then AChE spreads along the muscle fiber from the motor end plate. The data are consistent with the idea that there is a myogenic defect in the maturation of AChE regulation associated with the motor end plate of dystrophic chickens.