Studies determined the effects of granular chlorpyrifos on densities of nontarget arthropods in peanuts. A portion of several commercial fields was treated during the early pod stage of peanut growth in 1987 and 1988; then, densities of defoliating pests and arthropod predators were estimated weekly. Populations of Helicoverpa spp. were significantly increased in 1987 by chlorpyrifos application, but were not significantly affected in 1988. Densities of the velvetbean caterpillar, Anticarsia gemmatalis Hubner, were low on most sample dates. On dates when densities were great, populations were directly suppressed by chlorpyrifos application. Densities of the fall armyworm, Spodoptera frugiperda (J. E. Smith), were always low, and were not affected by chlorpyrifos application. Arthropod predators sampled included the red imported fire ant, Solenopsis invicta Buren; spiders (Aranaea: Araneidae); ground beetles (Coleoptera: Carabidae); earwigs (Dermaptera: Labiduridae); damsel bugs (Hemiptera: Nabidae); and bigeyed bugs (Hemiptera: Lygaeidae). Densities of spiders were significantly decreased by chlorpyrifos application. The other predators were not significantly affected. These results demonstrate that chlorpyrifos application results in nontarget effects on defoliating pest populations. Treated fields should be scouted regularly, because such fields may have an increased potential for outbreaks of some defoliating pests.