There is evidence that pheromones are communicative signals in animals. However, the existence and function of human pheromones are still under discussion. During the last years especially 4,16–androstadien-3-one (androstadienone), found in male and female sweat, became subject of intense investigation. Data suggest that androstadienone modulates our attention and the processing of visual cues. This thesis examines in three experimental studies the effects of androstadienone exposure in men and women on behavioral and cortical reactions to visual and emotional stimuli. The results corroborate the notion of androstadienone as an active social chemosignal. In minute amounts and not detectable as an odor it influenced brain responses and motoric reaction speed. This suggests that androstadienone indeed affects cognitive functions like attentional processes and in turn affects our behavior. Further androstadienone may act like a human modulator pheromone, namely modulating ongoing behavior and psychological processes to a particular context, by changing stimulus sensitivity, salience and sensory-motor integration.