The uptake of [ 3H]colchicine, which had diffused from silastic cuffs placed around the right sciatic nerve of adult rats, by extensor and soleus muscles was compared with amounts taken up into these tissues in animals treated with intraperitoneal injections of the drug. Each cuff contained 120 μg of [ 3H]colchicine, and animals injected with the drug received either one or two doses of 0.3 mg/kg body weight. About 39% of the [ 3H]colchicine diffused from the silastic cuff during the first 5 days and became widely distributed in the body; however, extrajunctional sensitivity to ACh, tetrodotoxin-resistant action potentials and membrane depolarization were recorded only in the ipsilateral (drug-cuffed) leg. The electrical and chemosensitive properties of the muscles in the contralateral (sham-cuffed) legs were unaltered. The [ 3H]colchicine content in that portion of the nerve enclosed by the cuff was 3.67 pmoles/mg wet tissue. This amount was about sixfold greater than that observed in sciatic nerves of animals treated with two intraperitoneal injections of the drug. The concentration of [ 3H]colchicine in extensor and soleus muscles of animals treated with the intraperitoneal injections was twofold higher than that observed in muscles whose nerves were exposed to silastic cuffs containing the drug. There were no signs of denervation (e.g., appearence of tetrodotoxin-resistant action potentials, membrane depolarization or appearance of extrajunctional sensitivity to ACh) in the muscles of animals injected with colchicine even though levels of the drug were higher in these tissues than that found in animals exposed to the silastic cuffs. Furthermore, simultaneous injection of colchicine intramuscularly had no effect on the level of extrajunctional ACh sensitivity of denervated muscles which were under constant direct stimulation. It is concluded that colchicine cannot produce signs of denervation by a direct action on the muscle membrane.