The phytotoxicities of three phenylurea herbicides applied annually to cotton at rates used for selective weed control were studied in irrigated soils of the southwestern United States. Yields of seed cotton were generally not affected by annual applications of 3-(p-chlorophenyl-1)-1,1-dimethylurea (monuron) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron). Annual applications of 3-phenyl-1,1-dimethylurea (fenuron) often reduced seed cotton yields. Mild chlorosis of foliage of cotton seedlings was occasionally observed when monuron was used annually. Although diuron affected the growth of oats and barley 6 to 12 months after application, it caused no adverse effect on cotton seedlings. Monuron residues affected barley and oats more severely than did diuron residues. Accumulation of diuron and monuron from annual applications at rates used for selective weed control in cotton appears unlikely.