Aquatic insects provide a critical energy subsidy to riparian food webs, yet their role as vectors of contaminants to terrestrial ecosystems is poorly understood.  We investigated relationships between aquatic resource utilization and contaminant exposure for a riparian invertivore assemblage (spiders and herptiles) along a stream contaminated with polychlorinated biphenyls (PCBs).  Stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes indicated that aquatic insect utilization varied among predators, with gradual enrichment of δ¹³C and depletion of δ¹⁵N as predators shifted from aquatic to terrestrial prey.  PCBs significantly increased with aquatic insect consumption as δ¹³C and δ¹⁵N explained 65% and 15%, respectively, of predator PCBs.  PCBs in predators were high, exceeding 2000 ng g^-1 (the human health advisory for fish tissue) in three species.  Greater consideration should be given to streams as lateral exporters rather than simple longitudinal conduits of contaminants.  Persistent contaminants are underutilized for addressing landscape-level questions in subsidy research, but our results demonstrate they are an ideal in situ tracer of stream-derived energy because they label stream organic matter over large distances.   Likewise, riparian predators like tetragnathid spiders have untapped potential as biological monitors of stream condition.