A bacterium which has the ability to degrade azo dyes has been isolated from a polluted environment and identified as Aeromonas hydrophilia. The specificity of azo dyes to the bacterium was examined. p‐Acetamidoazobenzene, p‐aminoazobenzene, acetanilide, aniline and p‐phenylenediamine, which are produced as metabolites, were also isolated.