The aim of this study was to evaluate the seasonal variation/geographical distribution of environmental concentration of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) across Poland using butter fat as an indicator of the contaminants. The average concentration of six indicator PCBs determined in the studied samples was 1500 pg g(-1) fat. The average concentration of 12 dioxin-like PCBs expressed as lower-bound dioxin-equivalent toxicity was 0.684 pg TEQ g(-1) fat. The average total concentration of 14 investigated PBDE congeners was 105 pg g(-1) fat. Statistically significant concentration differences between summer and winter samples were found. The results of this study indicate also a significant geographical diversification of butter contamination reflecting regional differences in environmental contamination. The seasonal variation of PBDE profiles evidences transformation of PBDE within the environment.