TASTE thresholds for the bitter substance PTC (phenylthiourea or phenylthiocarbamide) and related compounds containing the grouping (HNCS)showa bimodal distribution, leading to the designation ‘tasters’ for the more sensitive individuals and ‘non-tasters’ or ‘taste blind’ for the less sensitive. Genetic and population studies have generally attributed this to a simple Mendelian dominance system in humans, non-human primates and some rodent species. All other bitter and non-bitter compounds tested so far have produced Gaussian distributions of thresholds1,2. We have found now, however, that sensitivity to the taste of PTC predicts sensitivity to caffeine, a common bitter substance that lacks the HNCS grouping. This was shown by threshold measurements and magnitude estimation of supra-threshold concentrations.