A hypothesis that known sex differences in cognitive abilities reflect sex-related differences in physiology is offered. Females surpass males on simple, overleafried, perceptual-motor tasks; Wales excel oh mdre complex tasks requiring an inhibition of immediate responses to obvious stimulus attributes in favor of responses to less obvious stimulus attributes. It is hypothesized that these sex differences are reflections of differences in relationships between adrenergic activating and cholinergic inhibitory neural processes, which, in turn, are sensitive to the "sex" hbrmotles, androgens and estrogens. Studies Of the effects Of drug and hormone administration's oil these behaviors; dnd of sex hormones on adrenergic arid cholinergic neuro-transmitters are examined. Implications for cross-sectional correlative analyses of cognitive organization are discussed.