Biosorption of cadmium (Cd), cobalt (Go), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) by six fractions of particle sizes, ranging from 0.063 to 1.4 mm of dry marine algal biomass of Sargassum fluitans and Ascophyllum nodosum, is examined. Equilibrium metal uptake by larger particles was higher than that by smaller particles in the order of Pb > Cd > Cu > Co > Zn > Ni for both biomass types, with S, fluitans sorbing slightly more than A. nodosum. Uptakes of metals ranged from the highest, q(max) = 369 mg Pb/g (particle size 0.84-1.00 mm), to the low Zn and Ni uptakes, q(max) = 77 mg/g (size 0.84-1.00 mm) for S, fluitans. A. nodosum adsorbed metals in the range from q(max) = 287 mg Pb/g (particle size 0.84-1.00 mm) to q(max) = 73 mg Zn/g (particle size 0.84-1.00mm). Harder stipe fractions of S. fluitans demonstrated generally higher metal uptakes than the softer fractions derived from its blades (leaves). The pH dependence of the Zn uptake by S, fluitans exhibited a S-shaped curve between pH 1.5 and pH 7, with 50% of the maximum (pH 7.0) uptake at pH 3.5. Monovalent Na and K ions at higher concentrations inhibited the biosorption of Zn by S. fluitans. A significant inhibition started at 50 mM potassium chloride or sodium acetate, and at 1M the biosorption was completely blocked.