This paper describes the isolation of IPN-virus from a previously not recognised host fish. During routine diagnostic examination of laboratory-reared zebra danio( Brachydanio rerio )showing no signs of a disease, a cytopathic agent was isolated from the internal organs. The agent replicated in RTG-2 cells (but not in FHM-cells) with cytopathogenic effects (CPE) at 20 degrees C. The isolate was stable to treatment with chloroform and it was neutralized by IPN antisera. The neutralization test indicates that the isolated virus belongs to the IPN-virus group. This is the first report on the presence of IPN-virus in zebra danio.