The change in staining density of glial fibrillary acidic protein (GFAP) was analyzed in rats that sustained a chronic constriction injury produced by sutures tied loosely around one sciatic nerve. This injury model of peripheral neuropathy resulted in a behavioral hyperalgesia evidenced by a decrease in mean foot withdrawal latency to radiant heat. Increased GFAP immunostaining was observed in the gray matter of the spinal cord ipsilateral to the lesion and specific to spinal segments in which the sciatic nerve is distributed. Elevated GFAP staining density was attributed primarily to hypertrophy of astrocytes rather than their proliferation or migration since counts of astrocyte profiles demonstrated no significant difference when comparing the lesioned to the control side. The magnitude of the increase in GFAP staining correlated with the degree of hyperalgesia. Thus, these data suggest that astrocytes participate in the sequelae occurring in the dorsal horn following constriction injury of a peripheral nerve.