Otolaryngologists, neurologists and other medical practitioners are often not well equipped for assessing olfactory (dys)function. They either use no or inadequate olfactory tests. This problem of inadequate olfactory testing was systematically attacked by American psychologists in the early 80's and led to the construction of odour identification tests which are easy to administer. Combining the advantages of two of these American tests we developed a Dutch odour identification test (GITU), consisting of two subsets of 18 natural odourants and applicable in two ways: one for use in the ENT clinic, the other for industrial purposes. The first results of this test indicate that the incidence of serious olfactory disorder among adults in the Netherlands may be conservatively estimated at about 1%. The GITU readily discriminates between patients and controls and is sensitive to variables known to affect olfaction (gender, age). The recognition of olfactory dysfunction as a major problem has led in the U.S.A. to the establishment of clinical research centers for the study of human chemoreception. Evaluation results of four of those clinics together with data of three more case series--with a total number of patients of 4000--show that two thirds of all patients fall into three etiological categories: 1. Nasal disease and/or paranasal sinus disease. 2. Viral infection of the upper respiratory pathway. 3. Head trauma. For each of the three categories the literature is reviewed in order to arrive at a clearer picture of the olfactory patient with respect to age, gender, degree of olfactory deficit, spontaneous recovery, effectiveness of therapy and localization of the defect along the olfactory pathway. Finally an appeal is made to clinicians with interest in the subject to exchange more information with research scientists in olfaction. Such exchange is considered essential to making progress in this field.