A murine hybridoma cell line was obtained producing monoclonal antibody specific for human beta 2-microglobulin (beta 2m). The antibody reacts strongly with cell-associted human beta 2m, weakly with the cells of the monkey Cercopithecus aethiops, but not with any other non-primate cells tested. It is of IgG2a isotype, its pI is 6.9-7.1 and dissociation constant of its complex with soluble beta 2m is K = 1.5 X 10(-8) mol/l. The antibody also binds to beta 2m after electrophoretic separation under the reducing and denaturating conditions and blotting onto nitrocellulose. Immobilization of this antibody on Sepharose 4B yields an efficient immunosorbent for purification of beta 2m.