A method for detecting the onset of ovulation in a female mammal is provided. The method comprises contacting mouth air of the female mammal with an arylmethane test chromogen in an amount effective to undergo a rapid and detectable color change in the presence of one or more volatile sulfur compounds. The color of the test chromogen is compared to a control color that corresponds to a pre-ovulatory sulfur content. The difference in color between the test chromogen and the control color is correlated to the onset of ovulation.
