We have characterized segmental and laminar distribution patterns of Fos-immunopositive (Fos-IP) neurons in spinal cord segments L3–L6 after carrageenan treatment. A large number of Fos-IP neurons was found in the medial region of the ipsilateral dorsal horn laminae I–II at 4 and 6 h postinjection (pi). At one day pi, the number of Fos-IP neurons was decreased significantly, which correlated with suppression of inflammation in the affected hind paw. Bilaterally, Fos-IP neurons reappeared in the L3–L6 spinal cord segments at 3–4 days pi, mainly in the deep laminae LV–LVI. However, signs of inflammation had distinctly attenuated. Our data indicate a biphasic trend in Fos-IP in this experimental model of inflammation.