Adult female rats perinatally submitted to a protein deprivation schedule and then recovered with balanced chow, were tested under two different operant schedules of reinforcement, variable ratio-20 (VR-20) and differential reinforcement of low rate-5 sec (DRLR-5''). Undernourished animals showed higher response rates in the VR-20 schedule and a lower efficiency in the DRLR-5 as compared to controls, effects that could be attributed to the hyperreactivity to aversive or stressful situations characteristic of these animals. As the behavioral responses to anxiogenic stimuli are sensitive to drugs acting on the GABAergic system, the functionalism of the central GABAergic system in the undernourished group was evaluated by studying the reactivity to the anticonflict effect of diazepam in two conflict tests. Undernourished animals had a lower response to the anticonflict effect of diazepam when compared to control rats. The altered reactivity to the anticonflict effect of diazepam between both groups suggest that some aspects of the GABAergic neurotransmission may be involved in the behavioral abnormalities present in adult rats that were undernourished at perinatal age.