A strain each of mumps and Newcastle disease virus and five strains of influenza virus were found to be capable of removing all the receptors for this group of viruses from fowl red cells. Five virus strains were tested for their capacity to inactivate the virus hemagglutinin of human plasma and of egg white. In the case of egg white all strains including mumps and Newcastle disease virus inactivated the inhibitor completely, or nearly so. With plasma the influenza strains inactivated the inhibitor completely but mumps and NDV destroyed only that portion of the complex which effected mumps inhibition. The inhibitor for some strains was destroyed more rapidly than that for others and the sequence in which they were destroyed (inhibitor gradient) was similar, regardless of the strain employed. The inhibitor gradient for egg white was very different from that for plasma and these in turn differed significantly from the receptor gradient for fowl red cells.