Rats consuming a high-protein diet (HP; 50% casein) have increased locomotor activity, are hyper-responsive to nociceptive stimuli, and have increased basal arousal levels, as compared to rats maintained on a normal-protein diet (NP; 20% casein). The present study was performed to determine whether animals on the HP diet display deficits in learning, memory, and sensory discrimination. Male, Sprague-Dawley rats (4 months old) were divided into two groups and fed either the NP diet or the HP diet, ad libitum, for 32 weeks. Then the animals were observed in a variety of behavioral tests. In the swimming cylinder of Porsolt, which tests adaptation to stress, the HP group was significantly less able than the control group to develop an effective coping strategy (p < 0.05). When tested in the Morris Watermaze, animals on both diets performed equally well in the acquisition and recall of spatial information. During the recording of auditory evoked responses to deviant tones, short-term auditory memory traces degraded more quickly in the HP group than in the NP group (p < 0.05). These data suggest that rats fed the HP diet experienced deficits in short-term memory, associated with a diminished ability to cope with acute stress, whereas long-term memory was unaffected.