In monkey kidney cultures increments in infectious 2060 could be correlated with the degree of observed cytopathology. The absence of glutamine or vitamins contained in Eagle''s medium had some effect in lessening yield of infectious virus, but alterations in pH away from neutrality were more significant in reducing viral multiplication. Infectious 2060 was relatively unstable as evidenced by the inactivation rate at temperatures of 35[degree]C and above and pH below 5.0 and above 7.1. JH virus and 2060 were shown to be related antigenically, but were not identical, as shown by reciprocal neutralization titrations with animal and human antisera. Additional instances of neutralization titer increments in man following symptoms of mild respiratory illness have been presented.