The effects of sniffing different concentrations of the human sex-steroid derived compound 4,16-androstadien-3-one (AND) on autonomic nervous system function and mood were measured in 60 subjects. The effects were sex-specific and concentration-dependent. Only high concentrations of AND (0.00625 M) increased positive mood (p < 0.03) and decreased negative mood (p < 0.05) in women compared to men, and had sympathetic-like effects in women (p < 0.003), and parasympathetic-like effects in men (p < 0.05). These findings further implicate AND in chemical communication between humans, but pose questions as to the path by which AND is transduced, whether through chemical sensing or transdermal diffusion. (C) 2004 Elsevier Ltd. All rights reserved.