Abstract
A plaque count infectivity assay was developed in which chick cells infected with the Mount Elgon bat virus were completely resistant to superinfection with large doses of Sendai virus. Several variables markedly affected the assay sensitivity. The defined plaque assay was simple, highly reproducible and sensitive. It allowed determination of virus neutralizing antibody in a simple and reproducible test. Both actinomycin D and 5-iododeoxyuridine were without effect on plaque formation.