This paper presents the results of a survey utilising nitrogenstable isotope analyses to investigate the amount of dischargematerial (mainly municipal sewage) along the Istrian coast. Themain purpose of study was to measure the nitrogen isotope com-position of Patella sp. (P. caerulea) as a potential bioindicator fortracing anthropogenic pollution in the coastal marine environment.Further more, the objective was also to detect possible isotopicvariations between limpets of different sizes or between differentor ganism tissues.