Eleven strains of Acidovorax isolated from a freshwater lake and from healthy and diseased European eels in a hatchery were investigated by genotypic methods. DNA-DNA slot blot hybridization confirmed the identity of all strains as A. delafieldii. Isolates were heterogeneous in EcoR1 ribopatterns with four types recognizable. Most freshwater and healthy eel strains had the same ribotype but differed from the disease-associated strains. Typical ribopatterns of A. delafieldii contained 1·3, 1·5, and 3·2 kb fragments which provided useful additional taxonomic markers for species identification.