This paper is a review of progress in the ‘specific anosmia’ approach to the classification of odors. We have developed a suggestion by Guillot that the study of specific chemical defects in olfactory perception might reveal the fundamental or primary odors of the human sense of smell. Six varieties of specific anosmia have been mapped out in chemical detail. The maximum anosmic defects were observed with the following primary odorants: isovaleric acid, l-pyrroline, trimethylamine, isobutyraldehyde, 5α-androst-16-en-3-one and ω-pentadecalactone. We have named the corresponding primary odors: sweaty, spermous, fishy, malty, urinous and musky. There is evidence that other mammals may possess many of the same primary odor sensitivities. These primary odors appear to be well adapted for perceiving food and body odors, thereby conveying nutritional information and pheromonal signals in animals and man. Evidence from the known varieties of specific anosmia suggests that the total number of human primary odors is at least 32.