Barpress behavior was assessed in experimentally naive undeprived rats during exposure to three companion conditions: trained companion, untrained companion, and no companion. Non-nutritive sucaryl solution was presented as barpress-contingent reinforcement. Though overall levels of barpressing were low, the responding during exposure to either trained or untrained companions was significantly lower compared to the no-companion condition. This observation of companion-induced inhibition with undeprived rats compliments previous work testing socialfacilitation at high and low levels of thirst drive (Levine & Zentall, 1974). The findings also support the theoretical predictions of Zajonc (1965) regarding companion effects. According to the theory of social facilitation offered by Zajonc (1965). a companion can affect a subject in two basic ways. depending upon the subject's level of training on a particular task. The companion's presence was said to enhance performance of well-learned behavior and inhibit the performance of new responses (p. 270). In their study of companion effects with previously trained rats, Levine and Zentall (1974) raised an important argument with respect to Zajonc's theory of social facilitation (1965; 1968). Zajonc has assumed that the presence of a companion is a source of generalized drive. This generalized drive was offered as the causal factor in behavior changes as a function of exposure to a companion. Levine and Zentall have reported the effects of different levels of "basic" drive (thirst) on social facilitation. They found that the effects of thirst drive and the companion-induced drive summated. They tested four groups of rats: (l) high thirst drive with companion present. (2) low thirst drive with companion present, (3) high thirst drive with companion absent. and (4) low ·thirst drive with companion absent. Their results support Zajonc's theory . Groups where the companion was present performed significantly more barpressing compared to groups where the companion was absent . In addition. as would be expected, groups under the influence of high deprivation barpressed significantly more than groups under low deprivation . These two effects were obtained without a significant interaction of the two variables of drive and companion. The Levine and Zentall study showed that This pap er is sponsored by Hard y C. Wilcoxon. who takes full editorial responsibility for its conten t. Preparation of this manus cript was part ially supported by NICHHD Grant No. 00973. deprivation level can summate with companion­ induced drive . Thus, it follows that a better assessment of the effect of companion-induced drive will be obtained when subjects are not deprived at all. The present study measured barpressing in previously untrained rats during ' exposure to either trained, untrained, or no companion. Non-nutritive reinforcer was presented contingent upon bar ­ pressing. Where Levine and Zentall's work has shown the effects of high and low "basic" thirst drive on social facilitation. the present study sought to establish social facilitation effects for subjects not influenced by " basic" thirst drive . MEmOD