Two indirect ELISAs were developed to quantify specific antibodies in rainbow trout. One was against Yersinia ruckeri, agent of the ‘enteric redmouth disease’, in which a soluble antigen extract containing a high level of lipopolysaccharide (LPS) was used to coat microplates. The other was against Egtved virus, agent of viral haemorrhagic septicaemia, for which the virus was purified on sucrose gradients. In both cases the conjugate was a peroxidase-conjugated rabbit anti-trout immunoglobulin. The sensitivity and specificity of each ELISA were compared with agglutination and seroneutralization.