Porcine rubulavirus (LPMV) can establish persistent infections in porcine kidney cells. Cell cultures characterised at passages 25 and 65 demonstrated haemadsorption, formation of syncytia, and a slower growth rate. The nucleoprotein (NP) and haemagglutinin-neuraminidase (HN) protein were present in all cells, although not to the same extent as in wild type infected cells. Incubation of the cell cultures with virus neutralising antibodies could not cure them from the infection. The cells were resistant to LPMV high multiplicity superinfection, but lysed rapidly upon infection with VSV. These cells thus fulfilled the criteria of a true persistent infection. Viral particles were released into the medium from the persistently infected cells as measured by HA and infection of PK-15 cells with medium from the persistently infected cells. The infectious titer of the virus released from the persistently infected cells was 3 logs lower compared to wild type virus, the HN titer still being comparable. Virus released from the persistently infected cells was unable to cause a lytic infection in PK-15 cells, and showed a reduced ability to spread when compared to a LPMV lytic infection.