In the current issue of Science Bushdid et al. find that humans are able to discriminate at least 1 trillion olfactory stimuli. This finding far exceeds the previous estimates that humans can detect only 10,000 different odors. The authors used combinations of 128 odorous molecules to determine how many unique stimuli exist. They performed tests with human subjects to determine the discriminability of mixtures that varied in the percentage of odor components and from there applied a theoretical framework to determine the number of unique olfactory stimuli. They found a large discrepancy between the abilities of subjects to discriminate different mixtures, and they believe their estimate of 1 trillion distinguishable olfactory stimuli to be a conservative one.