Two different modes of cutaneous sensory reinnervation are thought to be engaged following nerve injury: regenerative growth of the injured nerve and 'collateral sprouting' of neighboring intact nerves. Although both processes are well known from experimental preparations, there is little unequivocal documentation of collateral sprouting in human skin. We report here on 5 patients in whom at least partial recovery of sensation in the hand following traumatic or surgical nerve section was apparently based on collateral sprouting from nerves that had not themselves been injured. Two types of evidence are brought. In three of the cases a totally anesthetic region of skin at a distance from the site of injury was shown to recover sensitivity long before regenerating nerve fibers could have arrived, given the known rates of fiber outgrowth. In the remaining two cases, nerve blocks using local anesthetics were used to establish that the reinnervated skin was served by a nerve other than the injured one. Thus, collateral sprouting appears to contribute to cutaneous sensory recovery in man as well as in animals.