The effects of neurotrophic factors on muscle protein degradation in rat leg muscle were studied. In order to inhibit axoplasmic transport and therefore transport of "trophic" factors, the colchicine cuff method of Albuquerque et. al. (1972) was modified so that the cuffs were cast in situ. Protein degradation was estimated by monitoring the release of tyrosine from the muscle. Our observations that colchicine cuffs increased tyrosine release are consistent with the concept of nerve-muscle trophism.