The present study investigated the effect of the endogenous steroid 4,16-androstadien-3-one (andro), a possible human pheromone, on attractiveness judgements of male and female voices and faces. 40 males and 39 females participated in a between-subjects, double blind study, evaluating the faces and voices of 60 donors while exposed to either andro masked in clove oil or to clove oil alone. In task 1, andro lengthened the time females took to classify voices as attractive or unattractive, and the time fertile females took to classify (especially male) faces as attractive or unattractive. In task 2, andro increased females' attractiveness and sex-typicality ratings of faces, effects that were limited to fertile females for voices. These findings provide support for the sex-specificity of andro's effects in a relevant social evaluation context, and highlight the role of menstrual cycle phase in regulating women's responses to the steroid. The sex-pheromone property of the compound remains unclear, however, since andro-induced attractiveness enhancement was not specific to male stimuli. Implications regarding alternative functions of the steroid are discussed.