trypsinised human o erythrocytes in the detection of rubellaspecific igm by sera fractionation on sucrose density gradient and absorption with staphylococcal protein a detection of rubella virusspecific igm employing trypsintreated human group o erythrocytes was evaluated using the method of sera fractionation on sucrose density gradients sdg and that of sera absorption with staphylococcal protein a the former method proved to be highly specific and sensitive in confirming or excluding rubella by demonstration of specific igm in contrast the latter method provided comparable results in only 7143 of specimens tested by both methods while falsepositive or negative igm results were obtained in the remaining 2857 of specimens in view of these results therefore it is recommended that all those specimens found positive for specific igm by the protein a method must be confirmed by another procedure possibly that of specific igm reduction with 2mercaptoethanol