A coho salmon Oncorhynchus kisutch (Walbaum) was found to develop lesions associated with so called X-cells propagating in the liver parenchyma. The ultrastructural features, insufficient to determine the origin of X-cells, corresponded to those found in pseudobranchial tumours of Atlantic cod by Watermann & Dethlefsen (Helgolander Meeresunters. 35: 231-242, 1982).