The effect deafferentation has on the morphology of giant interneurons was studied in the abdominal nervous system of crickets (Acheta domesticus). The morphology of four uniquely identified giant interneurons was exxamined by iontophoresing cobalt chloride into the neurons of interest. A major source of afferents for these interneurons consists of mechanoreceptors located on paired abdominal sensory appendages -- the cerci. Partial deafferentation of the giant interneurons was obtained by pinching off the cercus at hatching and maintaing the specimen in this deprived condition until adulthood. The interneurons of three groups of animals were examined; control specimens which were not treated surgically, unilaterally treated specimens which had a single cercus removed and bilaterally treated specimens which had both cerci removed. Two types of morphological changes were detected. (1) Chronic removal of a cercus was correlated with a reduction in length of dendrites ipsilateral to the ablated cercus; however, the general form of the dendritic branching pattern remained constant and recognizable. Two dendrites of a single neuron could be influenced independently if they were innervated by separate cerci. Thus deprivation did not have a generalized effect on growth of a neuron, rather it specifically influenced the dendrites deprived of afferents. (2) It was also observed that the projection of cercal sensory fibers in specimens reared with a single cercus differed from normal in that scattered fibers cross the midline in regions of the ganglion where none usually exist. It is suggested that modifications in the response properties of these deprived neurons are based on these two changes in morphology.