The amniotic sac of the chick embryo was much more effective than monkey kidney cultures for isolation of the Asian strain of influenza A, and virus was obtained from at least 60% of serologically diagnosed illnesses. Virus propagated both on monkey kidney culture and on chick embryo agglutinated human, fowl, sheep and monkey erythrocytes at 4[degree] or 24[degree] C, but titers were lower with sheep red blood cells. Asian virus multiplied readily in monkey kidney cultures, but several passages were required for adaptation to the allantoic sac. Some strains during early egg passages were not inhibited by non-specific substances in normal sera, and some were initially non-reactive with antibody, especially in rde (receptor destroying enzyme) treated sera. Increased sensitivity to inhibitors and antibody occurred with additional chick embryo passages, but remained less sensitive than the tissue culture line. Asian virus propagated in monkey kidney cultures was preferable to the egg line for determinations of hemagglutination-inhibition and neutralizing antibody by virtue of the higher titers, comparability of response and reproducibility.