Analyses of embryonic aneurogenic muscles indicate that several processes associated with early myogenesis in vivo proceed in the absence of peripheral nerves. However, aneurogenic muscles demonstrate impaired growth and limited survival. To investigate whether neurally mediated activity is responsible for these phenomena, aneurogenic muscles of the chick embryo were directly stimulated in vivo via implanted electrodes. Volumetric analyses of stimulated aneurogenic brachial (latissimus dorsi) muscles from Stage (St) 33 (7.5 to 8 days) through St 37 (11 days) demonstrated that growth was enhanced significantly beyond the level characteristic of unstimulated aneurogenic muscles. Moreover, for the majority of embryos, the stimulation regimen actually rescued the posterior latissimus dorsi muscle which characteristically does not survive beyond St 32 (7.5 days) in the aneurogenic state. Thus, our results implicate activity per se as an important factor necessary for the proper growth and survival of brachial muscles during early embryogenesis. The stimulation regimen, however, did not alter myosin ATPase profiles.