GABAergic neurons are found in all layers of cerebral cortex and display many types of non-pyramidal morphology. Most are intensely immunoreactive for neuron-specific enolase, suggesting a high rate of metabolic activity. The molecular layer and subcortical white matter are strikingly enriched in GABAergic cell bodies compared to other cortical layers. In rat, cat and monkey, many GABAergic neurons in the subcortical white matter and certain cortical layers are also immunoreactive for the neuropeptide somatostatin. Somatostatin content may define a widespread subclass of GABAergic neurons in mammalian cerebral cortex. Some may be similar in function to reticular neurons of thalamus.