• We investigated the adherence of T cells to human umbilical vein endothelial cells in seven patients with human T-lymphotropic virus type I (HTLV-I)—associated myelopathy. The adherence of T cells to endothelial cells increased significantly in all the patients with HTLV-I—associated myelopathy when compared with the adherence in the seronegative controls (1.3-to 2.8-fold) and compared with the adherence in the anti—HTLV-I—seropositive non—HTLV-I—associated myelopathy carriers (1.4- to 2.8-fold). Prior treatment of the endothelial cell monolayer with recombinant interferon gamma (50 IU/mL) enhanced the T cell—endothelial cell adhesion in both the controls and patients with HTLV-I—associated myelopathy. However, values after prior treatment in the patients with HTLV-I—associated myelopathy were significantly higher than those in seronegative controls and carriers. The results suggest that the significantly increased T cell—endothelial cell adherence may be related to the initial stages of lymphocyte migration from the blood to the central nervous system in patients with HTLV-I—associated myelopathy.