Human underarm secretions, when applied to women recipients, alter the length and timing of the menstrual cycle. These effects are thought to arise from exposure to primer pheromones that are produced in the underarm. Pheromones can affect endocrine (primer) or behavioral (releaser) responses, provide information (signaler), or perhaps even modify emotion or mood (modulator). In this study, we extracted underarm secretions from pads worn by men and placed the extract under the nose of women volunteers while monitoring serum LH and emotion/mood. Pulses of LH are excellent indicators of the release of GnRH from the brain's hypothalamus. In women, the positive influence of GnRH on LH affects the length and timing of the menstrual cycle, which, in turn, affects fertility. Here we show that extracts of male axillary secretions have a direct effect upon LH-pulsing and mood of women. In our subjects, the putative male pheromone(s) advanced the onset of the next peak of LH after its application, reduced tension, and increased relaxation. These results demonstrate that male axillary secretions contain one or more constituents that act as primer and modulator pheromones.