The putative human pheromone Delta4,16-androstadien-3-one (androstadienone), a non-androgenic steroid found in sweat and saliva, modulates psychological and physiological responses without detection as an odor. To investigate its modulation of psychological and neural systems, a series of investigations was conducted in which solutions of 250 muM androstadienone or clove-odor control carrier, on separate days, were applied to the upper lip of participants before experimentation. Fifty men and women completed three studies to specify psychological processes altered by androstadienone. Androstadienone accelerated speed to locate a probe appearing on the same side as emotional faces without affecting overall reaction times, indicating that it specifically enhanced automatic attention to emotional information. In a Stroop paradigm, androstadienone slowed ink color identification of emotional words, demonstrating greater allocation of attentional resources towards emotional information, with the cognitive (color) Stroop unaffected. Androstadienone did not alter attention to either neutral faces or shapes, tested during two continuous working memory tasks. These findings demonstrate that subliminal androstadienone guides psychological resources to specifically engage stimuli with emotional significance. An fMRI experiment examined how androstadienone modulated neural activity to produce these psychological effects. Passively inhaling androstadienone increased the BOLD response to emotional images (relative to neutral) in attention-related brain regions. Specifically, right orbitofrontal cortex, right lateral prefrontal cortex and right superior parietal lobule demonstrated greater activation to emotional images with androstadienone, as compared to the control session. Dynamic causal models revealed that androstadienone increased the drive from visual cortex to left amygdala, and to right amygdala specifically in women. Positive pictures additively enhanced these drives during the control session, but androstadienone diminished this increase. This decreased effect of positive stimuli accounts for androstadienone modulation of the frontal lobe response to emotional images, due to reduction of the inhibitory drive from amygdala to lateral orbitofrontal cortex. Finally, androstadienone's effect on attention to auditory emotional information was tested by examining the ability of twenty-four women to categorize emotional sentences (angry or sad) or neutral sentences (question or statement). Androstadienone did not alter performance for either sentence type, indicating that enhanced attention to emotional stimuli with androstadienone may be limited to the visual domain.