Anti-M is a relatively common naturally occurring antibody reacting optimally at 4°C and weakly or nonreactive at 37°C. It is usually clinically insignificant but can be active at 37°C because of thermal amplitude of IgM component or presence of IgG component. It can cause or delayed hemolytic transfusion reactions or hemolytic disease of newborn. At our center we have encountered two cases of anti-M antibodies- one presenting as crossmatch incompatibility and other as blood grouping discrepancy in the last 8 months.