Recombinant proteins representing full-length and truncated forms of the human immunodeficiency virus type 1 envelope protein gp160 were produced in E. coli and sf9 insect cells. These proteins were denatured and reduced as a function of purification. We adsorbed these proteins onto latex microspheres and used the protein-coated particles as a vehicle to present the antigen in vitro to splenic mononuclear cells from immune mice. Recombinant proteins presented on the latex particles induced antigen-specific proliferative responses that were dependent on the antigen concentration. The proliferative responses were similar to those produced against an identical protein used in soluble form and equivalent protein concentrations. Latex microspheres coated with recombinant proteins could also induce precursor cytotoxic T lymphocytes to mature to functional effector cells in vitro. The use of the latex microspheres to present recombinant proteins as antigens allowed for the use of denatured proteins in our assay that were not soluble in aqueous solutions, such as cell culture media. This system of delivering recombinant proteins in vitro should greatly facilitate the use of recombinant proteins in assays involving live cells.