An investigation of the behavior of different categories of disinfection byproducts (DBPs) in ultrapure water and in spiked drinking water samples was performed. The influence of sunlight, pH, and time was examined. Several of the compounds were subject to degradation with time, while others showed increasing trends, possibly due to natural production by bacteria. Chloroform, monochloroacetonitrile, and monochloroacetic acid slightly increased in the presence of sunlight, while d ichloroacetonitrile, dibromoacetic acid, tribromoacetic acid, and mixed bromo-chloro acetic acids were subject to decomposition, especially under sunlight. However, sunlight was found to decelerate decomposition of trichloropropanone and to prevent decomposition of bromochloro-acetonitrile and chloral hydrate. Trichloropropanone decomposed to chloroform, while mixed haloacetic acids decomposed to the corresponding trihalomethanes. Multiple regression equations were obtained for the concentrations of i ndividual DBPs in drinking w...