Individuals who are sensitive to the bitter compounds phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP) are also more sensitive to selected bitter and sweet substances, to sharp-tasting foods, and to the trigeminal irritant capsaicin. PTC/PROP tasters have a greater density of fungiform taste papillae and it is speculated that PTC/PROP tasters also have more trigeminal innervation. Because oral texture perception is also mediated, in part, by trigeminal fibers, it has been proposed that individual differences in fat perception might also be linked to PTC/PROP taster status and taste bud density. This work tests the hypothesis that individuals who are PROP tasters: 1. have a higher density of fungiform papillae; 2. are more sensitive to capsaicin; and 3. have increased ability to discriminate differences in fat content in salad dressing. Individual subjects were classified as PROP nontasters, medium tasters, or supertasters (n = 25 per group) by comparing their psychophysical function for PROP to that of NaCl. Papillae densities (papillae/cm2) were significantly different among the 3 taster groups (p < or = 0.0001), and were highest among the supertasters. Both medium tasters and supertasters perceived more oral burn from capsaicin than did nontasters at concentrations of 50, 70, and 100 ppm (p < or = 0.0001). Medium tasters and supertasters could also discriminate differences in fat content between 40% fat and 10% fat salad dressings (p < or = 0.005), but the nontasters could not. These data provide the first published evidence that fat perception can be linked to genetic and anatomical differences between individuals.