A rapid and sensitive procedure is described for the determination of trace amounts of eight substituted phenylurea herbicides. High-performance liquid chromatography is used, with an ultraviolet spectrophotometric detector. The herbicides are extracted from grain and soil samples with methanol and from water samples with dichloromethane. They are chromatographed on microparticulate silica bonded with octadecyltrichlorosilane using a mixture of methanol, water and ammonia as mobile phase.