A selectable retrovirus vector based on a full length HTLV-1 provirus clone, pCS-HTLV-1, was constructed by replacing the coding regions for tax, rex and the 3' region of env with the prokaryotic neomycin resistance gene under the control of the CMV promoter. This vector, pHTLV-1-CMVneo, was transfected into HTLV-1 infected human lymphocytes and fibroblasts. The production of recombinant virus by these cells was measured by the transfer of G418 resistance to target cells. Infection of target cells showed a preference for human lymphocytes in addition to two human fibroblast cell lines, Hos7 and RD4, and the African green monkey kidney cell line, Cos7. This system provides a method to study the cellular tropism of HTLV-1 and additionally provides a model to facilitate molecular studies of the natural events of HTLV-1 infection and integration.