Two experiments are reported in which cardiac habituation and dishabituation to pure tone stimuli were studied in well and malnourished Guatemalan infants. In both studies the magnitude of the orienting response was found to be attenuated or completely absent in infants suffering from nutritional insult. The findings were taken as evidence of a basic learning deficit that might account for the often reported poor performance of malnourished children on standard psychological tests. (Author/DP)