An analytical procedure is presented for the routine determination of trace amounts of ethoxylated nonionic surfactants in samples of raw and treated wastewater of sewage treatment plants. The alcohol ethoxylates were isolated by solvent sublation and Soxhlet extraction. Interferences were removed by open-column alumina chromatography. Following sample cleanup, the nonionic surfactants were derivatized with phenyl isocyanate and analyzed with RP-HPLC with UV detection. Sodium azide was used for preserving the environmental samples. Although the nonionic surfactants were isolated from the samples within 7 days, substantial losses (17-81%) were observed during transport and storage of the wastewater samples. Analytical recoveries of standard additions were >80%. The limit of determination of the procedure for effluent samples was 3.0 mu g/L. The concentrations of alcohol ethoxylates in samples of influent wastewater fluctuated between 1.0 and 5.5 mg/L, whereas concentrations between <3.0 and 12 mu g/L were found for effluent samples.