The plant growth stimulants ethylene dinitramine (EDNA) and ethylene have been reported to increase muscle regeneration. Such chemicals might therefore be of therepeutic benefit in the human muscular dystrophies. This report describes a series of experiments to reinvestigate the effects of EDNA, ethylene, and another plant-stimulating ethylene derivative, 2-chloroethylenephosphoric acid (Ethephon). EDNA and Ethephon administered two days after wounding both produced a significant increase of muscle protein synthesis seven days after the injury of normal muscle, though the increases were only 35 and 22%, respectively. The results suggested that early suppression of regeneration might explain the later increases. Ethylene administered in an identical way to that previously reported failed to increase muscle protein synthesis in murine muscular dystrophy or in wounded normal muscle. These studies suggest that treatment of human muscular dystrophies with ethylene derivatives is unlikely to prove of value.