Strains of Vibrio vuln~flcus biotype 2 were recovered from diseased European eels Angujlla anguilla during 2 epizootics These stralns were biochemically and serologically identical to the ATCC 33149 strain, which was lsolated from the Japanese eel Angujlla japonica. The isolates of biotype 2 from European eels were more virulent for elvers (LD50 < 10' cfu) than the Japanese strain used as control (LDS0 = 104 cfu). All strains of biotype 2 were able to adhere to human and fish cell lines and were also strongly cytotoxic. The extracellu1a1-products (ECPs) of the Japanese strain exhibited lipolytic, phospholipolytic, proteolytic, and haernolyt~c activities, whereas the ECPs of the Spanish isolates displayed only proteolytic activity. Strains of biotype 1 were recovered from tank water and healthy eels during the second outbreak. These isolates were biochemically similar to the type strain ATCC 27562, and serologically distinct from the isolates of biotype 2. Strains of biotype 1 produced proteases, haemolysins, and cytotoxins and showed specific adhesion to human cells, but they were non-pathogenic for eels. The strains of biotype 2 were more virulent for mice (LDS" = 10' to 106cfu) than the strains of biotype 1 (LDS(, = 10%fu), suggesting that this eel pathogen may also represent a health hazard problem for fish farmers.