The study took place on a portion of first category river of the Pas-de-Calais, along which exist 4 trout farms infected by the virus VHS and/or IHN. Electric fishing was carried out in June, September and October 1991 on 4 stretches up and downstream of the trout farms. This allowed a representative sampling of live fish other than salmonidae for virus isolation (85 analyses by batch of 3 or 5 individuals) and to realize 96 serological tests for VHS and IHN on blood samples of trouts captured in the river. About sixty serological tests were also made in each of the 4 fish farms in December 1991. As far as the river is concerned, all the virus isolations: and the serological tests were negative. Considering these results, the level of contamination and carriage of rhabdoviruses in the natural milieu connected with infected trout farms seems relatively low, but this does not rule out the possibility of transmission by wild fish.