Preemergent and postemergent herbicides were evaluated in the Mediterranean climate of the southern San Joaquin Valley and the desert climate of the Imperial Valley from 1998 through 2000. Sixteen herbicide treatments were applied both as preemergence (PRE) and postemergence (POST) applications to carrot (Daucus carota L.). Carrot was generally more tolerant to PRE herbicide applications than to POST applications. Carrot was tolerant to PRE and POST imazamox and triflusulfuron at both locations. Carrot root losses due to herbicide were consistent with visual ratings. Treatments that injured carrot tops early in the growing season did not always reduce yield at the end of the season. PRE applications of imazamox and triflusulfuron did not affect carrot tops or the number or weight of marketable carrots. Carrots grown in the Imperial Valley and in the San Joaquin Valley were tolerant to PRE applications of carfentrazone, sulfentrazone, and imazamox. Results were similar for POST applications, although carfentrazone slightly injured carrot roots. PRE application of herbicides increased forked roots more than POST. Chemical names used: α, 2-dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1, 2,4-triazol-1-yl]-4-fluorobenzenepropanoic acid (carfentrazone); N-[2,4-dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl]phenyl]me thanesulfonamide (sulfentrazone); N-(2 carbomethoxy-6-chlorophenyl)-5-ethoxy-7-fluoro (1,2,4) triazolo-[1, 5-c] pyrimidine-2-sulfonamide (cloransulam-methyl); 2-chloro-N-[(1-methyl-2-methoxy)ethyl]-N-(2,4-dimethyl-thein-3-yl)-acetamide (dimethenamid); (2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-(methoxymethyl)-3-pyridinecarboxylic acid) (imazamox); 3-chloro-5-[[[[(4,6-dimethoxy-2-pyrimidinyl) amino] carbonyl] amino] sulfonyl]-1-methyl-1H-pyrazole-4-carboxylic acid (halosulfuron); N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]-3-(ethylsulfonyl)-2-pyridinesulfonamide (rimsulfuron); (methyl 2[[[[[4-(dimethylamino)-6-[2,2,2-trifluoroethoxy)-1,3,5-triazin-2-yl] amino] carbonyl] amino] sulfonyl]-3-methylbenzoate) (triflusulfuron).