Canine distemper virus (CDV) was readily isolated at high rate with marked cytopathic effect (CPE) in B95a cells, a marmoset lymphoid cell line, from the peripheral blood leukocytes, cerebrospinal fluid cells and brain of dogs. Difference in type of CPE, i.e. syncytium type and round-cell one, among the virus isolates indicate the presence of heterogeneity of virus populations in prevalent CDV. Thus, this cell system is expected to be useful for ecological studies on CDV in the field.