Three different bioassays for analysis of biodegradable dissolved organic carbon (BDOC) were evaluated to identify which method is most applicable to analysis of drinking water. The determination of BDOC is primarily based on the differences between initial and final DOC levels during a certain incubation period using indigenous bacterial consortium as an inoculum. The assay procedures basically differ in the preparation method of inoculum. Inoculum was added in the form of suspended bacteria in one assay. In the other two assays, bacterial inoculum attached to either sand or inert media was used in a continuous reactor column. Standard solutions containing sodium acetate, sodium oxalate, or glucose at 1 mg C/L, and tap water were tested. The bioassay using bacteria attached to sand was shown to be superior to the two other methods for BDOC determination in terms of its incubation period, recovery, and reproducibility. Tap water samples, when analyzed by this assay, could not be guaranteed for biological stability due to their high BDOC concentrations (0.17 to 0.23 mg/L) that corresponded to 26-36% of the initial DOC level.