Monuron, 3–(p–chlorophenyl)–1,1–dimethylurea, is used extensively for weed control in asparagus. Growers apply approximately 1.5 lb/A of monuron in the spring before harvest begins, and the same amount in late June at the end of the harvest season. Each application usually controls weeds for 6 to 8 weeks. Since this chemical controls weeds for such a long period, growers are concerned as to whether, after continued use on the same soil for a period of years, this material might accumulate in the soil to the point where asparagus is injured, or the soil might be made unfit for crops which might follow asparagus. Therefore, a study was made of the persistence and penetration of monuron in soils of asparagus experiments where this chemical had been applied each year for a number of years.