The inflammatory response induced by mechanical lesion of the spinal cord is known to include the recruitment of neutrophils and macrophages, while the involvement of lymphocytes has been largely ignored. We have studied the pattern of lymphocyte recruitment following partial transection of the mouse spinal cord. Using immunohistochemical techniques, all three types of lymphocytes (CD4-positive T-cells, CD8-positive T-cells and B-cells) were found in the vicinity of the lesion site within hours and persisted for up to 7 days. There was a predominance of B-lymphocytes during the first 3 days. A second, late phase of cell infiltration, dominated by CD8-positive T-lymphocytes, occurred in mice that had been raised in a conventional breeding unit and had acquired antibody titres to a common murine virus (mouse hepatitis virus). In contrast, mice kept in specific pathogen-free facilities did not show this late-phase response. These findings suggest a possible role for lymphocytes in secondary tissue loss, local demyelination, scar formation, cytokine-mediated inflammatory responses or trophic processes. They also provide evidence that a virus infection can significantly enhance the reaction of T-cells to a spinal cord lesion.