In 1992-1993, 26 compounds and eight mixtures at a 1:1 ratio of some of these chemicals were tested for their toxicity to adults of a B-strain whitefly, Bemisia tabaci (Gennadius), in glass vials, in the Lower Rio Grande Valley of Texas. Synergistic, additive, or antagonistic properties of the compounds in mixtures were noted. Endosulfan + bifenthrin was the most toxic mixture tested; it was significantly more toxic than either of its components tested individually. Permethrin, lambda cyhalothrin, esfenvalerate, and Ciba 215944 (4, 5-dihydro-6-methyl-4-)3-pyridylmethyleneamino)-1,2,4-traizin-3((2H)-one), were more toxic than the other individually tested compounds; their LC 50 values ranged from 0.00095 to 0.0026 µg per vial. The growth regulators, fenoxycarb and buprofezin, were not toxic to adult whiteflies. Phosalone was the most toxic of seven organophosphorus compounds tested.