Constant and intermittent cold stressed juvenile northern bobwhite (Colinus virginianus) were exposed to chlorpyrifos, an organoiphosphorus insecticide following avian dietary LC(50) test procedures. Chlorpyrifos concentrations ranged from 100 to 1000 ppm; ambient temperatures included 35.0 (control), 32.5, 30.0 and 27.5 C. Survival decreased significantly under constant cold conditions. Non-survivors averaged 33% weight loss, but survivor weight dropped with increasing dose and decreasing ambient temperatures. Control quail at all temperatures maintained a constant body temperature (T(sub b)); however, T(sub b) of dosed quail fell with increasing dose and decreasing T(sub a). Non-surviving cold stress quail had higher cholinesterase (ChE) activity than non-survivors at 35 C; in addition, dead quail failed to average the 50% inhibition of ChE used to implicate a ChE depressant in death. Daily exposure of quail to 12h of warmth increased survival. Survivors of intermittent cold stress experienced less weight loss than constant cold survivors due to reduced metabolic costs. Synergistic effects were evident in juvenile northern bobwhite exposed simultaneously to chlorpyrifos and cold stress; however, mortality and certain sublethal effects were mitigated when cold exposure was intermittent. (Copyright (c) Elsevier Applied Science Publishers Ltd., England, 1987.)