Visual average evoked responses (AERs) to 4 intensities of light were studied in 5 patients with adrenal cortical insufficiency. Patients were tested off all medications, on ACTH while off all medications, and during replacement with carbohydrate-active steroids. Off treatment, when steroid levels were low, AERs were of small amplitude and short latency. Treatment with ACTH alone decreased the amplitude/intensity response, suggesting extra-adrenal effects. Both with amplitude and latency effects, stimulus intensity was an important parameter in determining steroid and ACTH effects.