Serums produced in guinea pigs or rabbits inocutlated with monkey (rhesuts or baboon) or human red cells contain the same high-incidence agglutinating activity found in human antiLW serumls. After one absorption with LW-negative blood cells. anti-LW specificity, was observed with stronger reactions on Rh-positive than Rh-megative cells. The 85-percent specificity was obtained after complete absorption with Rh-negative blood.