Though there are a theory of social facilitation and research data which suggest behavior will be enhanced in the presence of a conspecific, social inhibition of operant behavior does occur reliably in Japanese quail ( Coturnix coturnix japonica). Key pecking was assessed in 10 adult male quail during a series of episodes where a conspecific was either visible or not visible to the subject and each episode was either 10 sec., 60 sec. or 120 sec. in duration. Results indicated that consistent significant inhibition of responding occurred as a function of visual exposure to the companion; responding during sessions where durations of exposure were short (either 10 or 60 sec.) was significantly lower than that where durations were 120 sec., and interactions between the duration of exposure and visibility of a companion indicated that differences in duration were largely related to increased responding in the 120-sec. condition when the companion was not visible. There parametric findings serve further to define the conditions under which a conspecific can be a stimulus controlling learned behavior.