A natural secretion, 5 alpha-androst-16-en-3 alpha-ol (androstenol) is speculated to function as a spacing pheromone. The effect of the odor of androstenol on restroom-stall choices was investigated over a 5-week period. The first, third, and fifth weeks served as baselines against which the effect of androstenol or a control odor, 3 alpha-hydroxy-5 alpha-androstan-17-one (androsterone) could be evaluated. During the second and fourth weeks, half of the stalls in each restroom were treated with androstenol or androsterone, respectively. As predicted, men avoided the treated stalls during the androstenol week only, and neither odor affected female stall selection, demonstrating a sex differential influence of the experimental odor.