The within subject experimental approach of either doubling cortisone medication dose or withdrawing steroid treatment for 36 hr preceding behavioral testing was found to induce corresponding significantly elevated or suppressed plasma ACTH levels, as measured by radioimmunoassay, in six of eight adults diagnosed as having congenital adrenal hyperplasia (CAH). During the session characterized by elevated ACTH levels, the CAH patients exhibited significantly reduced median reaction times on the Sternberg Item Recognition Task. Their response pattern was suggestive of facilitated visual attentional functioning and/or overt motor response capacity rather than alteration of simple cognitive processing. Moreover, Sternberg performance was significantly correlated with endogenous ACTH levels but not with levels of plasma cortisol or cortisone replacement medication. This enhancement of performance paralleled a previous finding of improved performance on the Sternberg paradigm by normal adults following exogenous administration of ACTH 4-10 (Ward et al., 1979). Further analysis of the Sternberg performance suggests that other variables such as mineralocorticoid treatment, type of CAH impairment, and sex may act to moderate the degree of ACTH-related facilitation on this task. Performance on other visual and verbal attention and memory tasks, found earlier to be sensitive indices of exogenous administration of ACTH 4-10 and related fragments, was not significantly altered by manipulation of endogenous ACTH levels in these CAH patients.