Trichloroethylene (TCE) was hypothesized to produce free radicals which could be detected using electron paramagnetic resonance spectroscopy with the spin trap, PBN (alpha-phenyl tert-butyl nitrone). The free radicals detected following incubation of precision cut liver slices in media containing 10 mM PBN had hyperfine coupling constants aN = 1.61 mT and aH = 0.325 mT. There was a linear increase in free radicals detected in the bathing media when the headspace TCE concentration was increased from 2500-10000 p.p.m. The levels of conjugated dienes measured in the slices incubated in PBN supplemented media were less than slices exposed to TCE in incubation media without PBN. The PBN trap may act as a scavenger preventing the propagation of free radicals and inhibiting lipid peroxidation. The experiments suggest that free radical formation by TCE leads to a concomitant increase in conjugated dienes in liver slices which may contribute to the pathological changes which occur in liver following TCE exposure.