Bleached kraft effluent (BKE) is highly coloured due to the presence of high molecular weight, chlorinated, oxidised lignin. The dimethyl formamide-soluble portion of BKE was radiolabelled by methoxylation with14C-methyl iodide, and the resulting product (C14-BKE) was used to Investigate the mechanism of colour removal by fungi and bacteria. The white-rot fungiCoriolus versicolorandPleurotus sajor-cajudecolorised the solutions, and depolymerised the C14-BKE. Both fungi produced about 16Z14CO2from C14-BKE In 20 days. The three bacteria tested,Bacilluscereus and two strains ofPseudomonas aeruginosa, removed colour primarily by adsorption with little depolymerisation or mineralization. The adsorbed C14-BKE could be removed from bacterial cells by washing with 0.1 M NaOH.