Human T-cell lymphotropic virus I (HTLV-I) encodes for a 40-kDa protein, Tax, which is important for the immortalization of T cells. Tax has been shown to transactivate several cellular genes. In this study, we show that MIP-1α is selectively expressed and secreted in the tax transfected Jurkat cell line upon mitogen stimulation. Expression of MIP-1α-R mRNA in these cells suggests an autocrine role for this chemokine in HTLV-I infected T-cells. Induced MIP-1α expression and secretion in PMA/PHA stimulated tax transfected cells correlate with the noninduction of MNP-1 transcription factor, which is intimately involved in downmodulating the MIP-1α gene.