PURPOSE: To evaluate the size of the olfactory bulb using MRI in normal volunteers and anosmic or hyposmicpatients without nasal diseases. MATERIALS AND METHODS: MRI was performed in 20 normal volunteers with a normalsense of smell, and in 15 anosmic or hyposmic patients without nasal disease but with abnormality in the olfactoryfunction test. Coronal T1-weighted MRI was performed, with a section thickness of 3mm. The cross sectional area,width and height of the olfactory bulb were measured in multiple sequential images and the largest values of thesewere analysed. The difference in the size of the olfactory bulb between normal volunteers and anosmic or hyposmicpatients was evaluated and Student's t test was used for statistical analysis. RESULTS: In most cases, theolfactory bulb was demonstrated in three sequential coronal images; in normal volunteers, the largest crosssectional area, width and height were not significantly different between the right and left olfactory bulb. In 40 olfactory bulbs(right, left) in 20 normal volunteers and 30 olfactory bulbs in 15 anosmic or hyposmic patients,the respective means of various measurements were as follows: 7.5mm2 and 6.0mm2; greatest width, 4.6mm and 3.8mm;greatest height, 2.7mm and 2.0mm. For the largest cross-sectional area and greatest height, the difference inolfactory bulb size between normal volunteers and patients was statistically significant (P<0.01) but for thegreatest width, the difference was not significant (P>0.05). CONCLUSION: The size of the olfactory bulb issignificantly less in anosmic or hyposmic patients without nasal disease than in normal volunteers; in suchpatients, olfactory MRI could be a useful evaluative modality.