GABAA receptor binding is transiently increased in rat whisker barrels during the second postnatal week, at a time when neurons in the developing rat cortex are vulnerable to excitotoxic effects. To test whether these GABAA receptors might serve to protect neurons from excessive excitatory input, polymer implants containing the GABAA receptor antagonist bicuculline were placed over barrel cortex for a 4-day period in young (postnatal days 8 - 12) and adult rats. In the cortex of young, but not adult rats, the chronic blockade of GABAA receptors resulted in substantial tissue loss and neuron loss. The greater loss of neurons in young rats supports the hypothesis that a high density of GABAA receptors protects neurons from excessive excitatory input during a sensitive period in development.