Rapid development of different branches of industry and increasing human population have led to the release of various trace elements into the marine environment.Metal contamination,especially with mercury and its compounds,is believed to adversely affect marine organisms health.Marine birds due to fish consumption are exposed to accumulation of large amounts of methyl mercury(MeHg).This highly toxic pollutant adversely affects the reproductive,immune and central nervous system.Methyl mercury binds strongly with biological ligands containing sulfhydryl groups affecting the function of enzymes and interfering with protein synthesis.Because of this it has very high accumulative property through the food chain.The aim of this study was to determine the total and organic mercury content in liver,kidney and pectoral samples of marine piscivorous bird species(Razorbill – Alca torda,Black-throathed diver – Gavia arctica),which both winter in the south part of Baltic Sea and Gulf of Gdańsk.Birds had been collected from 2006 to 2011,which in majority had drown in fishing nets.Birds were divided on two age groups: juveniles(up to 1 year)and adults(more than 1 year).Among both species were male and female individuals.Total mercury content was determined by cold-vapor AAS technique at 253.7 nm wavelength.Extraction of samples with HBr and toluene followed by back-extraction to L-cysteine solution enabled determination of organic mercury with the same technique as for total mercury.The distribution of total mercury among organs is similar in both species,with the highest concentrations for liver and for kidney.Liver and in lesser extent kidney plays crucial role in detoxification process.Lower values of total mercury were found for pectoral muscle.The same pattern can be observed for methylmercury.Significantly higher values of total mercury were found for gavia arctica than for alca torda.In case of alca the higher concentrations were found in adult than in juvenile individuals which can indicate the occurrence of bioaccumulation.For black-throathed diver individuals the concentrations were on the same level which can be due to low number of adults.The same pattern can be observed for methylmercury.There were significant differences in total mercury content in relation to individuals which were collected in different seasons of the year,with higher values for spring than for autumn.