Fifteen minutes after the initiation of swimming stress in the rat we observed a 50% increase in the number of [3H]RO 5-4864 binding sites in kidney and a 37% increase in the olfactory bulb, without change in affinity. The binding in heart and cerebral cortex remained unchanged after the stress. These results are discussed in relation to previous work on both the action of an acute stress in central benzodiazepine receptors and the possible modulation of peripheral benzodiazepine receptors of the kidney by adrenocortical hormones.