Despite the increased research and regulatory interest in numerous bioactive agents, including natural hormones, xeno-hormones and pharmacological agents, little is known about the presence of these compounds in the estuarine and marine environment. In this study, the results of a 2-year survey on the occurrence of the natural female sex hormones, estradiol (E2) and estrone (E1) and the synthetic steroid, ethinylestradiol (EE2) in the Scheldt estuary (Belgium-The Netherlands) are presented. Chemical analysis of the water samples was performed using Speedisk extraction. Suspended matter samples were analyzed with accelerated solvent extraction (ASE) and detection was performed with gas chromatography coupled to multiple ion trap mass spectrometry. Detected concentrations were in the low ng L(-1) range. E1 and betaE2 (beta-isomer of E2) were detected in water and suspended matter, whereas concentrations of EE2 were below the limit of quantification (LOQ). E1 was observed most frequently and at concentrations up to 10 ng L(-1) in water and up to 0.84 ng g(-1) in suspended matter samples.