HTLV-I, the causative agent of Adult T cell Leukemia, has recently been found to be associated with chronic neuromyelopathies common in tropical areas and in Japan. We report here the establishment of a lymphoid T cell line from peripheral blood lymphocytes of a patient with Tropical Spastic Paraparesis. This cell line produces a retrovirus whose morphologic, antigenic and genetic characteristics show no detectable difference from the leukemogenic prototype of HTLV-I.