The hydrothermal deep-sea vent fauna is naturally exposed to a highly specific environment enriched in potentially toxic species such as sulfides, metals and natural radionuclides due to the convective seawater circulation inside the oceanic crust and its interaction with basaltic or ultramafic host rocks. However, data on radionuclides in biota from such environment are very limited. An investigation was carried out on tissue partitioning of Po-210 and Pb-210, two natural radionuclides within the U-238 decay chain, in Bathymodiolus azoricus specimens from the Mid-Atlantic Ridge (Menez Gwen field). These two elements showed different distributions with high Pb-210 levels in gills and high Po-210 levels in both gills and especially in the remaining parts of the body tissue (including the digestive gland). Various factors that may explain such partitioning are discussed. However, Po-210 levels encountered in B. azoricus were not exceptionally high, leading to weighted internal dose rate in the range 3 to 4 mu Gy h(-1). These levels are slightly higher than levels characterizing coastal mussels (similar to 1 mu Gy h(-1)). (C) 2010 Elsevier B.V. All rights reserved.