When polluted waters containing high concentrations of ammonia-nitrogen and organics are treated with prechlorination, the excessive dosages of chlorine required produce chloroform and other trihalomethanes in the finished water. In an attempt to avoid the use of prechlorination, packed-bed filtration alone and packed-bed filtration preceded by ozonation were studied side by side. The results indicate that packed-bed filters using coke and gravel as the media can remove >90 percent of the ammonia-nitrogen when the volumetric loading is <300 g NH+4-N/m3.d. Organics are also removed, but to a lesser extent. Ozonation did not seem to significantly improve the performance of the biological filters. The dissolved oxygen content of the water was important in controlling the performance of the filters. In general, packed-bed filtration was found to be effective for reducing the dosage of chlorine needed for prechlorination. (NOTE: An erratum correcting part A, Figure 4 of this article appears on p. 4 of the September 1993 Journal AWWA.) Includes 16 references, tables, figures.