Alkylphenol polyethoxylates are a major class of nonionic surfactants that are microbially degraded in sewage treatment plants (STPs) and sediments to more toxic and hydrophobic alkylphenols. Recent data on the estrogenic activity of alkylphenols has prompted interest in the distribution of these compounds in the aquatic environment. Sediment samples were collected from several sites (n Ο 28) at industrialized and pristine regions of Lake Huron, Lake Erie, and Lake Ontario, USA and Canada, and analyzed for concentrations of 4-nonylphenol (NP) and 4-(tert)-octylphenol (OP). Also, sludge samples were taken from a secondary STP in Whitby, Ontario, Canada. Sediment and sludge samples and analytical standards were prepared for analysis by gas chromatography-mass spectrometry in selected ion mode by combined acetylation and supercritical fluid extraction. Concentrations of NP were up to 37 g/g in sediments and ΟΎ300 g/g in the sewage sludge. Concentrations of OP were up to 23 g/g in sediment and 21 g/g in the sewage sludge. These data indicate that alkylphenols are distributed widely in sediments in the lower Great Lakes. However, concentrations of NP were present at high (g/g) levels only in sediments near urban and industrialized centers.