Keratinous tissues of mammals and humans, such as hair, have been used to determine the exposure to polychlorinated biphenyls (PCBs) and organochlorine pesticides. In the present study, we investigated the accumulation of persistent organic pollutants (POPs; PCBs, p,p'-DDT, p,p'-dichlorodiphenyldichloroethane [DDD], p,p'-dichlorodiphenyldichloroethylene [DDE], hexachlorobenzene [HCB], oxychlordane, trans-nonachlor, polybrominated diphenyl ethers, and polybrominated biphenyls [PBBs]) in feathers of the great tit (Parus major). The accumulation of POPs in feathers and fat samples of 27 adult great tits collected in April 2000 and December 2002 was compared with regard to possible temporal and spatial differences. Polybrominated diphenyl ethers, PBBs, trans-nonachlor, and HCB could not be quantified in feathers. Most PCB congeners and DDTs (p,p'-DDE, p,p'-DDD, and p,p'-DDT) could be determined in feathers, although concentrations in feathers were markedly lower (sigmaPCB concentration range, 28.2-87.1 ng/g) than concentrations in fat (sigmaPCB concentration range, 1244-10074 ng/g). Feathers had relatively higher levels of low-chlorinated PCBs (tetra- and pentachlorinated biphenyls) and p,p'-DDD compared to levels in fat, presumably reflecting levels in blood. Persistent organic pollutant concentrations did not increase with the age of the feather, suggesting that exogenous or aerial depositions of POPs onto the feather surface had no, or only minimal, influence on levels in feathers. For almost all compounds studied, POPs in feathers and fat were significantly positively correlated in samples collected during the breeding season but not in samples collected during the winter. This temporal difference may have been caused by seasonal changes in lipid reserves. Although further research is required, feathers appear to be a promising new, nondestructive biomonitor for PCBs and DDTs in avian wildlife.