Olfactory adaptation exerts its influence in almost all aspects of the functioning of the sense of smell. An adapted olfactory sense is characterized by elevated odor thresholds, reduced responses to suprathreshold sensations, slower reaction times to odors, and, sometimes, a shift in perceived odor qualities. The presence of trigeminal properties (i.e., pungency) in an odorous stimulus slows the adaptation process. Studies of olfactory adaptation, perhaps even more than any other aspect of human smell function, need to control for subject bias and expectations. Presently, standardized clinical tests of olfaction do not include an olfactory adaptation component, largely because of practicality considerations. Recent reports show that aging speeds olfactory adaptation and slows recovery. In view of this, it might prove revealing to explore olfactory adaptation in patients with diseases known to affect the sense of smell and compare the results with those obtained in matched control subjects.