A Baikal seal (Phoca sibirica) was experimentally infected with Baikal seal morbillivirus (BSMV) isolated from Baikal seals during an epizootic in 1987-1988. The seal was infected with BSMV with an infectious titer of 10(7.0) TCD50/ml, and daily observations of the animal clinical condition were made. The virus-specific antibodies in the seal serum were determined by ELISA and virus neutralization test. The clinical picture showed a mild infection. The ELISA-active antibodies were detected 10 days postinfection and reached the maximum in 20 days. Virus-neutralizing antibodies were detected in 16 days after infection, reached the maximum titer of 1:640 in 20 days and remained at this level for 39 days (the observation period). These data indicate that BSMV can induce a disease in the natural host with production of virus-neutralizing antibodies. The results of this work and the earlier reports show that the epizootic in Baikal seals was induced by BSMV.