Monobrominated PCBs(Br-PCBs) are known to exhibit dioxin-like effects and to be more toxic than their PCB counterparts. In this study, Br-PCBs are reported, to our knowledge for the first time, in biological samples, specifically in juvenile ringed seal (Phoca hispida) from the Baltic Sea. Mass spectrometric techniques (ECNI and EI) have been employed to gather structural and elemental composition information, respectively, in the absence of authentic reference standards. Quantification indicates total levels of Br-PCBs at a minimum of 20 ng/g extractable lipids. A technical PCB (Clophen A50) was investigated and also found to contain Br-PCBs, the results of which were compared to those from seal. Technical PCBs are thus possible environmental sources of Br-PCBs occurring in seal. Other potential sources are also discussed.