Following high-frequency stimulation of hippocampal dentate granule cells, potentiation was difficult to achieve in undernourished animals, showed a significant decline within 3 to 6 hr, and was completely absent at 24 hr. Further trains of stimulation resulted in only small benefits in undernourished animals. Coupled with previously reported morphological and behavioral deficits, these findings indicate a marked hippocampal dysfunction resulting from early undernutrition and provide a potentially valuable approach for relating nutritionally induced behavioral impairments to brain function.