In the current study, the use of spraints for monitoring levels of polychlorinated biphenyls (PCBs) in individual otters was experimentally validated. On the basis of a detailed pattern analysis, it is concluded that in the current study, PCB concentrations in spraints that contain relatively high concentrations of nonmetabolizable PCB congeners (PCB 138 and 153 > 42.5% of total PCB concentrations) reflect the internal PCB concentrations of the otter that produced the spraint. In general, however, spraints should be selected that contain relative concentrations of PCB138 and PCB153 > 95th percentile of these congeners in samples from local food items of otters. On the basis of relationships between levels in spraints and internal levels and on earlier reported effect concentrations, a threshold level range of 1.0 to 2.3 microg/g (lipid normalized) in such spraints is proposed. The validated methods to monitor PCBs in otters may be combined with genetic marker techniques that can assess the identity of the otter that produced the spraints. In such a design, it is feasible to monitor PCB levels in individual free-ranging otters in a truly animal friendly way.