The research described here investigated the effectiveness of activated carbon adsorption for the removal of polychlorinated biphenyls (PCBs) and toxaphene from organic-free water (OFW) and humic acid background solution, using bench-scale equilibrium and rate tests. In addition, complexation experiments were conducted to assess the extent of association between the target pollutants and humic acid (HA). The dispersed-flow homogeneous surface diffusion model was satisfactory for predicting the performance of fixed-bed adsorbers for removing PCBs from OFW. When HA was present, carbon capacity was greatly reduced because of complexation and competitive adsorption effects, and the adsorber dynamics were complicated by the presence of various species such as unassociated HA and pollutant-HA complexes. Includes 25 references, tables, figures.