The paper discusses the identification of organic disinfection byproducts (DBPs) at a pilot plant in Evansville, IN, which uses chlorine dioxide as a primary disinfectant. Unconventional multispectral identification techniques (gas chromatography combined with high- and low-resolution electron-impact mass spectrometry, low-resolution chemical ionization mass spectrometry, and Fourier transform infrared spectroscopy) were used to identify more than 40 DBPs in finished water at a chlorine dioxide pilot plant in Evansville, IN. Treatment variations included the use of liquid versus gaseous chlorine dioxide and the use of residual chlorine. Among the more unusual compounds identified were a series of maleic anhydrides, which are believed to have been formed from maleic acids during the extraction and concentration process, and halopropanones. (Copyright (c) 1994 American Chemical Society.)