Two isolates, N3 and T 3 were cultivated in various cell cultures, and the infective titers of extra-cellular virus, intra-cellular virus were determined in every other period of 5 days. From those growth curves of the isolated viruses, We have known the pertinent cell line cultures are RK-13 and ESK. Virus titer reached 10,.0-.., TC!D50/0. 1ml at 12 to 24 hours postinoculating in RK-13 cell line and 107,0-..s TCIDso/0. l ml at 24 to 48 hours postinoculating in ESK cell line. Virus titer reached around l06·a-c·7TCID50/0. lml at 24 to 96 hours postinoculating in PK-15, AuBEK, BK, MK, and KB cell lines.
The pathogenicity of the two isolates were weakened for rabbit after 20 subpassages in RK-13 and ESK.