The activity concentrations of radionuclides (60Co, 54Mn, 137Cs, 40K) in whole plants of Fucus vesiculosus of different ages, and also in tissues of different ages from the same plants were investigated in the vicinity of the Barsebäck nuclear power plant in southern Sweden. Activity concentration differed between the tissues of different age of the plants, depending on the radionuclide as well as the time of year. The highest concentrations of 60Co and 54Mn were measured in the older parts of the plants in spring and summer, while the activity concentrations of 137Cs and 40K were highest in receptacles and new vegetative fronds. The discharge of radionuclides from the nuclear power plant was reflected in the measured activity concentration in the algae. For 60Co, the response seemed to be smoothed out when considering the whole plant, while the new vegetative tissue better reflected the discharge during the autumn. Thus, it is important to have knowledge about the autecology of the organism when it is used as an indicator for radionuclides.