Bobwhite quail (Colinus virginianus) that received either 0, 2, 4, or 8 mg/kg methyl parathion (O,O-dimethyl o-p-nitrophenyl phosphorothioate) treatment were investigated as to their susceptibility to predation by a cat (Felis domesticus) predator. Four hours after receiving methyl parathion (MP), physical activity levels were monitored in quail and included the number of seconds spent still, walking, running, or flying before and after a cat was introduced into an experimental arena. The cholinesterase (ChE) activity for each quail on experiment was determined. Quail that were captured exhibited significantly greater inhibition of brain ChE activity and spent significantly more time being still than noncaptured birds. Birds receiving MP at 8 mg/kg spent more seconds being still than those in other treatment groups and had ChE activity reduced to 42.8% of normal activity. There was a tendency for quail at increasing treatment levels to be more susceptible to capture by the cat predator. The neurological and behavioral effects of methyl parathion may have important ecological ramifications.