The aim of this study was to compare the indicator properties of Fucus vesiculosus and Ascophyllum nodosum. Activity concentrations of 137Cs, 40K, 7Be, 228Ra, 99Tc, 90Sr and $^{239,240}$Pu were measured in plants of the two species collected monthly in 2002 from one location at the southeastern coast of Norway. For 40K, 137Cs, 90Sr, 7Be and 228Ra the activity concentrations were significantly higher in Fucus vesiculosus than in Ascophyllum nodosum, whereas the opposite was the case for 99Tc. For 137Cs, 90Sr, 7Be and 228Ra the temporal variations in activity concentrations showed similar pattern for the two species, whereas for 99Tc the temporal pattern was different for the two species. The observed temporal variations in activity concentrations of 137Cs (both species) and 90Sr (only Fucus vesiculosus) correlate with expected variations in seawater concentrations. For 137Cs salinity, light conditions, temperature and growth rates seem to work in the same direction as the variations in seawater concentrations. A lack of correlation between salinity and 99Tc concentrations in the algae indicates a slower dynamic in uptake and/or secretion for technetium. The observed differences between the two species may partly be explained by the difference in growth rate and life length between the two species.