The production, function, and use of a new antiglobulin control cell is described. The cells are sensitized with monovalent Fab (fragment, antigen‐binding) fragments and can be agglutinated by active antiglobulin serum only. In contrast to commercial antiglobulin control cells, which are frequently associated with false‐positive results, the reactivity of the Fab‐sensitized cells is entirely specific. It is concluded that Fab‐sensitized cells provide greater quality assurance than currently available r