Author Posting. © The Authors, 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Environmental Pollution 157 (2009):2345-2358, doi:10.1016/j.envpol.2009.03.024. ; Concentrations of several congeners and classes of organohalogen contaminants (OHCs) and/or their metabolites, namely organochlorine pesticides (OCs), polychlorinated biphenyls (PCBs), hydroxylated-PCBs (OH-PCBs), methylsulfonyl-PCBs (MeSO2-PCBs), polybrominated diphenyl ether (PBDE) flame retardants, and OH-PBDEs, were measured in cerebrospinal fluid (CSF) of short-beaked common dolphins (n = 2), Atlantic white-sided dolphins (n = 8), and gray seal (n = 1) from the western North Atlantic. In three Atlantic white-sided dolphins, cerebellum gray matter (GM) was also analyzed. The levels of OCs, PCBs, MeSO2-PCBs, PBDEs, and OH-PBDEs in cerebellum GM were higher than the concentrations in CSF. 4-OH-2,3,3’,4’,5-pentachlorobiphenyl (4-OH-CB107) was the only detectable OH-PCB congener present in CSF. The sum (Σ) OH-PCBs/ Σ PCB concentration ratio in CSF was approximately two to three orders of magnitude greater than the ratio in cerebellum GM for dolphins. ; This study was supported through an Environmental Protection Agency STAR fellowship (U-91616101-2) and a National Woman’s Farm and Garden Association Scholarship awarded to Dr. Eric Montie, and by the WHOI Ocean Life Institute, the Quebec Labrador Fund/Atlantic Center for the Environment, the WHOI Academic Programs Office, the Sawyer Endowment, Walter A. and Hope Noyes Smith, and Dr. David Mann at the University of South Florida.