Some adult humans cannot detect the odor of androstenone (5 alpha-androst-16-en-3-one), a volatile steroid. To test for the presence of genetic variance associated with this trait, adult twins were tested for their ability to smell androstenone and another odorant, pyridine, that is readily perceived by most adults. Ascending concentration, two-sample (odor versus blank) forced choice tests were used to assess sensitivity to these odorants. Intraclass correlations for identical and fraternal twin detection thresholds to pyridine were small and not significantly different. However, intraclass correlations for thresholds to androstenone were significantly different, with the correlation for identical twins being greater than that for the fraternal twins. These data indicate a genetic component of variation in sensitivity to this odor. Investigations that use genetic variation could offer a new tool for studies of olfactory transduction mechanisms.