Abstract Ronstar EC (emulsifiable concentrate) was applied at rates of 4.48 or 8.96 kg ai/ha as a broadcast spray during the winter, in late spring, and in mid-summer to plots in commercial hop fields. Residues of oxadiazon, the active ingredient, and its 4 metabolites (methoxy, alcohol, acid, and phenol) were determined at harvest (1 month after last treatment) in green and dry hops and in hop foliage, by using gas-liquid chromatography after column chromatographic cleanup. Drying the cone increased residues of oxadiazon, but resulted in loss of the methoxy and alcohol metabolites. Oxadiazon residues in hop foliage ranged from 0.058 to 0.163 ppm. Measurable amounts of metabolites were also found in the foliage.