A semiautomated extraction and cleanup method has been developed for the measurement of eight polybrominated diphenyl ethers (PBDEs), 2,2',4,4',5,5'-hexabromobiphenyl (BB-153) and 2,2',4,4',5,5'-hexachlorobiphenyl (CB-153). The method employs automated addition of internal standards ((13)C-labeled), addition of formic acid (denaturation agent), and dilution with water prior to automated overnight extraction using a modular solid-phase extraction (SPE) system. Removal of coextracted biogenic materials was performed on a two-layered 3-mL disposable cartridge containing activated silica gel and a mixture of silica gel and sulfuric acid. Sample cleanup was automated using the same modular SPE system. Reproducibility and precision of the liquid handler used for internal standard additions were shown to be 2 and 4%, respectively. Overall reproducibility during processing of eight batches of samples (N = 30/batch, including methods blanks) was below 10% for most analytes. Mean recoveries of the (13)C-labeled internal standards ranged from 69 to 95% for the seven monitored PBDEs; 76 and 98% were recovered for BB-153 and CB-153, respectively.