A moderately halophilic species of Halomonas sp. degraded 0.1 g phenol/l as the sole source of carbon and energy in a model industrial saline waste-water with NaCl-concentrations varying between 1 and 14% (w/v) NaCl and exhibited optimum growth on phenol at about 5% (w/v) NaCl. However, the degradation of 0.1 g phenol/l by Halomonas sp. at NaCl-concentrations < 5% (w/v) was accompanied by the accumulation of an intermediate of the ortho-cleavage pathway, later on identified as cis, cis-muconic acid.