The efficacy of using hair as a biomarker for exposure to polybrominated diphenyl ether (PBDE) flame retardants was assessed in humans and an animal model. Paired human hair and serum samples were obtained from adult men and women (n = 50). In parallel, hair, serum, liver, and fat were collected from adult male Sprague-Dawley rats exposed to increasing doses of the PBDE mixture found in house dust for 70 days via the diet. All samples were analyzed by GC-MS for eight common PBDEs: BDE-28, -47, -99, -100, -153, -154, -183, and -209. Paired human hair and serum samples had five congeners (BDE-28, -47, -99, -100, and -154) with significant individual correlations (0.345-0.566). In rat samples, BDE-28 and BDE-183 were frequently below the level of detection. Significant correlations were observed for BDE-47, -99, -100, -153, -154, and -209 in rat hair, serum, liver, and fat across doses, with r values ranging from 0.803 to 0.988; weaker correlations were observed between hair and other tissues when data from the lowest dose group or for BDE-209 were analyzed. Thus, human and rat hair PBDE measurements correlate strongly with those in alternative matrices, validating the use of hair as a noninvasive biomarker of long-term PBDE exposure.