Cell membrane components bound to β2-microglobulin were isolated from Renex 30 (a nonionic detergent)-solubilized membrane materials of two human T cell-type cell lines, MOLT-4 and CCRF-CEM, by gel filtration and lectin affinity chromatography. The isolation was carried out by following the β2-microglobulin activity by radioimmune inhibition assay. The T cell membrane components bound to β2-microglobulin had a uniform molecular size of about 200,000 daltons and most of them showed an affinity to lentil lectin. The isolated membrane components were radioiodinated and examined for identity to HLA antigens by sequential precipitation with rabbit anti-HLA antiserum (specific to HLA large components) and with rabbit anti-β2-microglobulin antiserum. In addition to HLA antigens, the β2-microglobulin-bound components obtained from the MOLT-4 cells were found to contain certain membrane components that are the same in molecular size as the HLA large components but that are different antigenically from the HLA large components. On the other hand, the β2-microglobulin-bound membrane components obtained from the CCRF-CEM cells were all HLA antigens. No other membrane components were involved in the binding.