A number of methods have recently been developed to measure the biodegradability of aquatic natural organic matter. These techniques measure assimilable organic carbon, biodegradable organic carbon or bacterial growth potential. This article reviews the various methods involving biomass and dissolved organic carbon (DOC) and summarizes their application to the assessment of treatment processes and bacterial growth in distribution systems. Studies comparing the methods are summarized; they generally show good qualitative correlations among biodegradability measurements. However, none of the methods can be considered ready for routine use. Research and development needs are identified. Includes 57 references, tables, figures.