The subcellular accumulation of Cd in different tissues of the marine gastropod Nassarius reticulatus was determined following exposure to 0.1, 0.3 and 0.9 mg Cd/litre seawater (nominal concentrations) and the importance of cytosolic Cd-binding components for the sequestration and immobilisation of the metal evaluated. Different tissues from exposed whelks were removed, pooled, homogenised, the homogenates subjected to subcellular fractionation and fractions measured for Cu, Zn and Cd by atomic absorption spectrophotometry. Cytosols were further separated and heat-stable Cd-binding capacity determined. All subcellular fractions in different tissues accumulated Cd at all exposures. The total cytosolic protein concentration in some tissues was strongly affected, but there was no concentration-dependent increase in Cd-binding capacity of the heat-stable protein pool. The major cytosolic Cu- and Cd-binding components in all four tissues were low molecular weight (Mr 5-10 kDa), whereas most cytosolic Zn coeluted with components of very low molecular weight.