Field and experimental observations on sea anemones (Actinaria) Ammonia viridis (Forskål) and Actinia equina (L.) indicated that in both species body zinc concentrations usually ranged between 100 and 200 ug (g dry wt)1 in waters containing up to 200 μg I1 of the metal. At higher dissolved concentrations, as observed in Restronguet Creek, A. equina exhibited only slightly enhanced tissue levels. However, in the laboratory, zinc levels in Anemonia viridis increased markedly at sea-water concentrations exceeding 200 μg I”1. Studies on the uptake of 65Zn-labelled zinc showed that, when the sea-water concentration was increased from 2 to 52 μg 11, both species absorbed the metal and new equilibria appeared to be reached in about a week. At equilibrium, the concentration of zinc in Actinia equina had risen by up to 11%, and in Anemon ia viridis, by up to 28%. About one third of the difference between the amounts absorbed by the two species may be accounted for by zinc accumulated in the symbiotic algae (zooxanthellae) of A. viridis. Short-term (12 h) experiments showed that, although A. viridis absorbed a significant amount of labelled zinc when the concentration increased from 2 to 52 μg I1, uptake was not much greater when the concentration increased from 2 to 202 μg I1. It is postulated that, up to a sea-water concentration of 202 μg I1, the absorption of zinc is dependent on the amount adsorbed at the body surface: saturation of the surface at higher concentrations leads to more direct dependence on the level of dissolved zinc.