The level of the acid DNase activity in the hemocytes and digestive gland of the mussel Mytilus galloprovincialis after exposure to model marine pollutants, a detergent, gasoline and a copper salt, as well as to unknown environmental mixture at selected sampling sites, was investigated. The specific enzyme activity in unexposed mussels from mariculture area was higher in hemocytes than in digestive gland. Concentration and time effect patterns of DNase activity revealed tissue- and pollutant-specific responses to model marine pollutants. Since in some cases the pollutant effect could not be detected by measurement of acid DNase in single tissue only, digestive gland/hemocyte (Hep/Hem) ratio was introduced. The Hep/Hem ratio enabled the detection of pollutant effect at the significance level. Field investigations indicated that the digestive gland is a suitable tissue for discrimination of polluted areas from maricultured area. Additionally, the Hep/Hem ratio enabled differentiation within a group of polluted sampling sites that differ in the type of pollutants and/or environmental conditions.