Mussels (Mytilus galloprovincialis), clams (Venerupis decussatus) and oysters (Crassostrea gigas) were sampled seasonally during 2004-2005, from different coastal environments of Morocco in order to measure their accumulated heavy metal concentrations. The concentrations of Hg and Pb were determined by AFS and ICP-MS methods, respectively, whilst the remaining metals (Cd, Cr, Cu, Mn, Zn and Ni) were quantified by AAS. The soft tissue concentrations of the mussels were on average 7.2 mg kg-1 (Cd), 9.6 mg kg-1 (Pb), 0.6 mg kg-1 (Hg), 26.8 mg kg-1 (Cu), 8.8 mg kg-1 (Cr), 292 mg kg-1 (Zn), 20.8 mg kg-1 (Mn) and 32.8 mg kg-1 (Ni). The highest tissue heavy metal concentrations were recorded in the south from the industrial area of Jorf Lasfar. The relationships between metal concentration and season in each species showed very similar annual profiles with a peak observed around spring-summer. Statistical analysis indicated that different species showed different bioaccumulation of metals depending on study site and season. The accumulated metal concentrations in bivalves from the clean stations may be considered as useful Atlantic coast reference background levels for future comparison.