Splenocytes from BALB/c mouse immunized with potato virus X (PVX) and myeloma cells (SP/2) were fused. After cloning and three screening cycles, three hybridoma cell lines secreting strain-specific monoclonal antibodies (MCAs) against PVX were obtained. These cell lines were stable for 20 generations and after storage in frozen form (in liquid nitrogen) for one year. The chromosome numbers of the three hybridoma cell lines clustered in the 92-102 range. The MCAs all belonged to the IgG3 immunoglobulin subclass. The medium supernatant antibody titer detected by indirect ELISA was 1:320-1:640. The mouse ascites antibody titer was 1:102,400-1:204,800, which was more than 300 times the rabbit antiserum titer (1:320). The MCAs had a neutralizing effect on the antigen, with neutralization titer of 1:10(2). There were no apparent changes in antibody activity after repeated freezing/thawing cycles, ammonium sulfate precipitation, or freeze-drying.