Ether treatment was studied as a method of increasing the ability of type B influenza antigen to detect antibody by hemagglutination inhibition. Comparisons were made with the untreated antigen, with an eluate made from the same virus, and with a standard type B antigen of an earlier virus. Results were evaluated based on the comparative ability to detect rises in antibody titer, as well as the relative frequency of antibody prevalence determined by each method. The ether-treated antigen was far superior to the untreated antigen in both respects; it was also superior to the eluate, although the difference was less pronounced. The treated antigen performed better than the standard type B antigen in detecting antibody in children, but there was little difference in adults. This pattern was felt to be a result of the closer relation of the treated antigen to the infecting strain. The method is, therefore, proposed as a means of producing more reactive antigens of currently circulating strains of type B influenza virus.