There is convincing evidence from numerous studies using both psychophysical and electrophysiological approaches that olfaction is markedly reduced in Parkinson´s disease (PD). Data on the prevalence of olfactory dysfunction in PD however, range from 45% and 49% in the pioneering studies of Ansari & Johnson, and Ward, respectively, up to 74% in the work of Hawkes et al., or as high as 90% in a study published by Doty et al. Quality of life, safety, and interpersonal relations, as well as food behavior/nutritional intake are severely altered in a large proportion of patients with olfactory loss. Thus, the same can be assumed in patients with Parkinson's disease. If it was possible to improve olfactory function this would appear as a significant effect in patients with Parkinson's disease. Provided the study would reveal an improvement of olfactory function following therapy with rasagiline, this would have tremendous worldwide impact on the use of this drug. Considering the frequency of PD a very large number of patients would benefit from these findings, especially in terms of quality of life.