Bromide and natural organic matter in water are known to play a role in the formation of ozonation byproducts. Their exact effect on the production of various ozonation byproducts was examined in this bench-scale study, which used ranges of bromide and dissolved organic carbon (DOC) concentrations typical of US waters. Results show that bromate and cyanogen bromide formations are a function of bromide and DOC concentration, with the effect of bromide being more significant. On the other hand, the formation of aldehydes and ketoacids was proportional to the amount of DOC in the water, but they were largely unaffected by bromide concentration. In addition, the ozone dosage needed to achieve the target ozone residual increased with DOC concentration. Includes 21 references, tables, figures.