Although some patients initially present with a frank complaint of a smell disturbance, others are unaware of their dysfunction or are extremely inaccurate in assessing its magnitude, pointing to the need for routine quantitative olfactory assessment. Olfactory threshold measures have been the most common means for assessing smell function quantitatively. Unlike threshold tests, suprathreshold tests employ clearly discernible stimuli. Among such tests are those of odour identification, recognition, discrimination, memory and attribute scaling; the latter employs, for example, rating scales and magnitude estimation procedures. In the case of olfactory threshold measures, tests based upon forced-choice procedures are more reliable than those based upon non-forced-choice procedures. As with educational and psychological tests, the reliability of an olfactory threshold test is generally a function of test length, with greater reliability occurring the more frequently the threshold region is sampled.