The first recorded isolation of a paramyxovirus from a bat (Chiroptera) is described. The isolate was subsequently identified as a new animal subtype of the parainfluenza type-2 group. Pathogenicity for suckling mice, chick embryos, and 3-day-old white leghorn chicks was demonstrated. Growth in two primary cell cultures and several cell lines was characterized by the formation of syncytia having a “Swiss cheese” appearance. Seroepidemiologic studies revealed specific neutralization of the bat virus by serum specimens from 5 of 70 fruit-eating bats, Rousettus leschenaulti. Bat parainfluenza antibodies were also demonstrated in 10% of the human serum samples tested, but they were not present in sera from Macaca monkeys.