The size of colonies growing on Sabouraud's dextrose agar (SDA) supplemented with 1 microM beta estradiol (1,3,5-estratiene-3,17B-diol) was compared to those growing without the estrogen supplement. Data (video pixel counts) were obtained by video capture and image analysis and revealed that yeast strains were not uniformly stimulated by estradiol. One estrogen-responsive strain was evaluated in a chemically defined medium to evaluate growth in the presence of 17-alpha and 17-beta isomers of estradiol. The beta isomer promoted more rapid growth of the test organism and resulted in greater biomass production than the alpha isomer. Understanding of the role of mammalian hormones as growth promoting signals may provide information on this organism's shift from saprophytic to commensal to pathogenic status in vivo. Strain variation in response to estrogen may provide an explanation for differences in virulence.