Abstract The sense of smell significantly contributes to quality of life. In recent years much progress has been made in understanding the biochemistry, physiology and pathology of the human olfactory system. Olfactory disor- ders may arise not only from upper airway phlogosis but also from neurodegenerative disease. Hyposmia may pre- cede motor signs in Parkinson’s disease and cognitive deficit in Alzheimer’s disease. These findings suggest the complementary role of olfactory tests in the diagnosis and management of neurodegenerative diseases. In this report we present a review of modern olfactory tests and their clinical applications. Although rarely employed in routine clinical practice, the olfactory test evaluates the ability of odour identification and is a useful diagnostic tool for olfaction evaluation. Olfactory screening tests are also available. In this work we strongly recommend the impor- tance of an ENT evaluation before the test administration and dissuade from a self-administration of an olfactory test. Key words Neurodegenerative disorders • Smell • Olfactory test • Hyposmia Introduction Unlike auditory and visual sensory systems, the sense of smell has always been undervalued. Many questions about olfactory anatomy and physiology remain unanswered. This explains the low interest of physicians in smell disor- ders. It is well known that the sense of smell plays an important role in quality of human life. It provides for pro- tection from dangerous substances like spoiled food and polluted environments and it determines the flavour and palatability of foods and drinks. Normal variations of the olfactory function include the strong genetic basis of the ability to identify odours [1], better and longer ability of women than men to identify odours [2, 3], significant decrease of the ability to identify odours after the seventh decade of life [3, 4] and the compromise of olfactory func- tion in urban residents and some workers [5]. Disorders of the sense of smell may be typically intermittent or perma- nent. When hypo-anosmia is intermittent there are usually some conditions that interfere with the access of the odor- ant to the olfactory neuroepithelium (transport loss). Conversely, an injury of the receptor region (sensory loss) or damage to the central olfactory pathways (neural loss) cause a permanent olfactory dysfunction. Prior upper res- piratory infections [6], head trauma [7] and nasal and/or sinus diseases [8] lead to smell dysfunction but frequently the cause of the olfactory loss remains unknown (idiopath- ic smell dysfunction) [9]. Disorders of olfactory function have also been associated with exposure to toxic chemicals [10], tobacco smoking [11], endocrine disorders (hypothy- roidism, diabetes, Kallmann’s syndrome, renal failure and liver diseases) and neuro-psychiatric diseases. Among these, Alzheimer’s disease (AD) is one of the earliest to be reported and studied in detail [12, 13]. Many studies have shown an early olfactory identification deficit in AD prob- ably because the processes of odour identification involve medial temporal lobe structures which are affected in the early stages of AD, while the ability to detect odours is affected later [13–15]. Several other neurological disorders Neurol Sci (2005) 26:147–155 DOI 10.1007/s10072-005-0452-3 A. Eibenstein • A.B. Fioretti • C. Lena • N. Rosati • G. Amabile • M. Fusetti Modern psychophysical tests to assess olfactory function ORIGINAL Received: 12 December 2004 / Accepted in revised form: 16 June 2005 A. Eibenstein • A.B. Fioretti • C. Lena • N. Rosati M. Fusetti () Surgical Sciences Department, ENT University of L’Aquila Piazza S. Tommasi 1, I-67100 L’Aquila, Italy e-mail: marco.fusetti@libero.it G. Amabile Department of Neurology and ENT University of Rome “La Sapienza”, Rome, Italy