The ability to smell varies greatly between different individuals. Some people are unable to detect an odor that most people can smell. It is not known what causes these individual differences. Humans have about 1000 genes for odorant receptors that bind and detect odor molecules. It has been shown that some of these genes exist in two forms: a functional one and one that has been mutated and is therefore no longer functional. We think that people who can not smell a specific odor may carry the non-functional form of the gene for the receptor that detects the odor molecule. To test this hypothesis we want to find people who can not detect a specific smell and then compare their odorant receptor genes with those of people who can smell the odor.