Quantitative receptor binding autoradiography was used to study the NK1, NMDA, 5HT1a, and 5HT2 receptor binding densities in the adult rat lumbar spinal cord from 3 days to 20 weeks following a unilateral crush lesion of the sciatic nerve. NK1 binding density increased unilaterally in the superficial dorsal horn on the side of the sciatic crush to reach levels 60% above controls by 4 weeks following the lesion and returned to control values by 12 weeks. NMDA binding density increased bilaterally and equally in both the dorsal and ventral horns to reach 300% of control values at 2 weeks following the crush and returned to near control values by 20 weeks following the lesion. Serotonergic receptor binding did not change. The changes in NK1 receptor binding density on postsynaptic dorsal horn cells are consistent with a response to the decrease and recovery in the synthesis and transport of tachykinins by the dorsal root ganglion cells following peripheral nerve injury. the bilateral changes in NMDA receptor binding are more likely mediated by polysynaptic pathways in the spinal cord that respond to the changes in metabolic events of the dorsal root ganglion cells evoked by axotomy and regeneration.