This paper provides first hand information on the metal biosorption by capsulated and decapsulated cells of field and laboratory-grown unicellular cyanobacterium Microcystis. Field-grown capsulated Microcystis showed a higher biosorption efficiency than the decapsulated laboratory-grown one. A higher adsorption capacity of capsulated field and laboratory-grown Micrycystis was further confirmed by respective high K-f values of 2.161 and 1.976 for Fe3+ than 1.761 and 1.569 for Cu2+. Biosorption maxima (saturation) for Fe3+ and Cu2+ were obtained respectively after 20 and 60 min; the rates for biosorption of two metals being 27.04 mu g Fe3+ mg(-1) min(-1) and 3.31 mu g Cu2+ mg(-1) min(-1). In the bimetallic combination of Fe3+ and Cu2+, Fe3+ was more efficiently biosorbed than Cu2+. Application of Freundlich and Langmuir isotherms offered support to a multilayer binding for Cu2+ and monolayer for Fe3+. This study suggested that the naturally abundant biomass of otherwise nuisance Microcystis holds great potential for use as biological biosorbent in the removal of heavy metals.