The cellulose industry produce chlorophenols as a result of the use of chlorine during pulp cellulose bleaching, and are discharged into natural waters by their effluents. The pollution of coastal sea waters by chlorophenols and several other organic compounds could modify the biota of this environment because the compounds have high toxicity, are recalcitrant, and are accumulated in sediments or at different levels in the trophic chain (Fleming 1995). Despite the toxic properties of chlorophenols , many bacteria isolated from natural environments are tolerant to various concentrations of these chemicals, and some strains have demonstrated the ability to degrade these molecules (Saber and Crawford 1985). In addition, the enzymes involved in chlorophenol degradation and their genetic origin have been reported (Cork and Khalil 1995). The Arauco Gulf posses a high biological productivity, despite its contamination with chlorophenols due to industrial effluents discharging. This environment has demonstrated stability to the impact of contaminants (Acuna and Chuecas 1994), and the basis for this behavior is still being studied. We investigated the effect of chlorophenol on bacterial viability using a population of aerobic heterotrophic bacteria isolated from coastal sea water near a discharging cellulose pulp mill. The aim of this work was to determine if chlorophenol tolerant bacteria or degradative bacteria may contribute to the stability of the Arauco Gulf ecosystem.