The effect of short-term denervation on the response to insulin was studied in isolated rat soleus and extensor digitorum longus (EDL) muscles 6 and 24 h after severing one sciatic nerve. Impaired insulin sensitivity and response occurred within 6 h postdenervation in solei. After 24 h, EDL of fed and fasted rats and solei of fed rats showed no stimulation of glycogen synthesis even with supraphysiological doses, whereas solei of fasted rats showed markedly decreased sensitivity and response to insulin. Insulin resistance of glycogen synthesis represented impaired stimulation of glucose transport and impaired glucose-independent activation of glycogen synthase by insulin. Changes in initial glycogen content of muscles did not correlate with insulin resistance. Insulin binding after denervation showed only minimum impairment and did not account for the marked insulin resistance. The response of denervated solei to epinephrine was unimpaired. Insulin resistance, which develops early after denervation in red and white muscles, represents primarily a defect in receptor-function coupling, suggesting that in muscle, nervous stimuli and/or contractile activity modulate signal transmission by the occupied insulin receptor.