The adsorption and desorption of diquat and paraquat on eight arid-zone soils were studied. Adsorption of the two organic cations on the soils conformed quite well with the linear form of Langmuir equation. Practically the adsorption maximum of a given soil for diquat may be considered similar to that of paraquat. The adsorption maxima obtained for the eight soils ranged from 17 to 47 me/100 g. The CEC of a soil was found to be the determining factor of diquat (r= 0.946) and paraquat (r = 0.932) adsorption.The strong adsorption capacities of the soil ranged from 9 to either 23 or 21 me/100 g for diquat or paraquat, respectively. This corresponds to a range of 1930 to 4500 tons/ acre-in. for diquat or paraquat, respectively. It was thus concluded that these herbicides do not constitute any residue hazard.Less than 1 percent and about 50 percent of the adsorbed organic cations could be released with water and 1 M BaCl2, respectively, from the two soils considered.