Rabbits were infected with Legionella pneumophila by intravenous administration of allantoic fluid from eggs infected with this organism. Heated plasma from animals with severe illness caused by L. pneumophila lysed erythrocytes from guinea pigs in a radial hemolysis assay. Plasma from control rabbits did not lyse guinea pig erythrocytes in parallel assays. Urine from two of the infected animals also showed hemolytic activity. Attempts to induce illness in rabbits by intranasal administration of L. pneumohpila were less successful. Allantoic fluid from embrynated hen eggs developed hemolytic activity when maintained eithr in vitro at room temperature or in eggs whose embryos were killed by refrigeration. Hemolytic activity in filtrates of allantoic fluid from eggs infected with L. pneumophila, as previously reported, may not be due to the presence of bacterial hemolysins in the fluid.