In the course of an investigation into the health of eels on a commercial eel farm in England, IPN virus was isolated. This is the first isolation of IPNV from eels in the United Kingdom, and was considered to be of interest because the Serotype was Ab, whereas most IPN virus types in the U.K. are Sp. The farm received elvers from one of two common collecting sites, and they had been on the farm for about 1 year and were in good condition, with no clinical abnormalities. Eels collected from the same source, but on different farms were negative for IPNV. Further investigation revealed that an import of small eels from France had been held on the farm for a short while but, at the time of our investigation, had been transferred elsewhere. The farm utilises industrial warm water effluent (22 degrees C), originally taken from a nearby river. We screened a cross-section of species of wild fish from the river, including salmonids. These all were negative for IPNV. The source of the infection remains unknown.