The adsorption of two polymeric Surfactants on an organic pigment was investigated. As surfactants the anionic polyacrylic acid sodium salt (PANa, M-W = 15,000) and a non-ionic block copolymer surfactant based on styrene oxide (SO) and ethylene oxide (EO) (MW = 1500) were used. The adsorption behavior was analyzed by size exclusion chromatography of the supernatant after centrifugation of the pigment dispersions. It was found that PANa has no affinity to the pigment, whereas SO-EO has a strong affinity to the pigment surface. Competitive adsorption of PANa and SO-EO was not observed. Addition of SO-EO yields stable dispersions. (C) 2008 Elsevier Inc. All rights reserved.