Across a wide range of nonhuman vertebrate species, males react to stimuli from potential mates with both courtship behaviors and transient, short-onset increases in luteinizing hormone and testosterone. Research in our lab is investigating whether and how such reactions may occur in human males. An initial study (Roney, Mahler, & Maestripieri, 2003) found that men's salivary testosterone increased 20 minutes after the onset of a brief conversation with a young woman, and that testosterone change scores were correlated with the conversation partners' ratings of how much the men were trying to impress them. Ongoing research in the lab is attempting to replicate and extend this finding with additional manipulations of women's behavior, variations in timescale of measurement, and examination of whether cortisol responses are also affected by such stimuli. Positive results could support the possibility that human mating psychology is regulated in part by brain pathways that are homologous to those found in nonhuman vertebrate species.