Eleven monoclonal anti-IgG antibodies were evaluated by ten laboratories for possible AHG reagent use by the ISBT/ICSH protocol. Three of the anti-IgGs were selected by tests with weak Fya sensitized cells as this represents the best screening test. One of the IgM class anti-IgGs (205) equalled ISBT/ICSH reference reagents (R3P and RIIIM) against weak anti-D, -K and Fya sensitized cells and it reacted with all four subclasses of IgG. Thus, subject to satisfactory stability and extended trials with a wide range of weak antibodies, monoclonal anti-IgGs for AHG reagent use are now a possible alternative to conventional rabbit anti-IgG.