The distribution of 5-HT1, 5-HT1A, 5-HT1B and 5-HT2 receptors in the rat spinal cord was investigated with quantitative autoradiography. Receptors were labeled respectively with [3H]serotonin (5-[3H]HT),8- hydroxy-2-[N-dipropylamino-3H]tetralin (8-OH-[3H]DPAT), [125I]iodocyanopindolol and [3H]ketanserin. It is shown that 5-HT1, 5-HT1A and 5-HT1B receptors are distributed within the spinal cord according to a rostro-caudal gradient. Both 5-HT1 and 5-HT1A receptors are mainly present in the dorsal horn and 5-HT1B is present throughout the spinal cord, exhibiting high densities in the caudal-most part of the dorsal horn in lamina X and in the sacral parasympathetic area. On the other hand, 5-HT2 receptors are shown mostly in the thoracic sympathetic area and in the thoracic ventral horn; the dorsal horn exhibits few 5-HT2 receptors. The differential involvement of 5-HT through different receptors in nociception, autonomous nervous system control and motility are discussed.