Wastewater contains trace amounts of antibiotics as well as other pharmaceuticals.  During chlorine disinfection, pharmaceuticals react with chlorine and form transformation products, some of which may retain the properties of the parent molecule.  We are testing the properties of the products that form with antibacterial activity assays and identify the product with high performance liquid chromatography coupled with mass spectrometry (HPLC/MS).  Doxycycline forms products with antibacterial activity.  The formation of the products is more prominent in clean water than in wastewater effluent matrix due to selective competitive reactions between chlorine and either organic matter or doxycycline.  Testing of other antibiotics is planned in the near future.