The present review discusses the current knowledge of the molecular pharmacology and neuroanatomical and subcellular localization of both the central benzodiazepine/GABA-chloride ionophore receptor complex and the peripheral benzodiazepine receptor. It then reviews all of the literature to date on how these two receptor sites are modulated by environmental stress. The possible role of these sites in learning and memory is also discussed. Finally, a theoretical model is presented which examines the differential, and perhaps complementary, alterations of these two sites in an organism's response to stress.