Investigated conditions leading to the intragastic (IG) reinforcement effect in a lever-pressing situation in which oral stimulation and IG injections of a liquid diet could be controlled independently. Male and female albino Wistar rats served as Ss in 3 experiments. Ss lever pressed only when an oral stimulus was available to mediate the effects of food injections and not for the oral stimuli or injections alone. Using a 2-bottle choice technique it was shown that the value of oral stimuli can be enhanced by liquid diet injections. It is concluded that IG injections of food have the power to enhance the value of oral stimuli, but do not reinforce operant behavior directly. (15 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)