Carrots were grown in trifluralin-treated soil and sampled over a 6-week period beginning 6 weeks after seeding. The residue of pesticide and principal metabolite in the carrot was measured by both 19 F NMR and GC-ECD. The trifluralin concentration was observed to decline from 0.3 to 0.03 mg/kg. Although there was excellent agreement between the two methods at all levels for the parent compound, in general, only the GC method was sensitive enough to measure the low concentrations of the metabolite