Tobacco use creates a tremendous burden on the health care system and is the largest non-communicable source of disease globally. Olfactory bulb was the structure in the ventral surface of the brain which receives olfactory input data and also known to involve in the regulation of basic behaviors. This study was carried on 75 domestic rabbits with a mean weight of 1500-2000gm from January 2011- August 2011 in Ain Shams university. These rabbits were divided into three groups as follow: Group I:

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... Included 25 rabbits that received fresh food and water. Group II: Included 25 rabbits were injected subcutaneously with 1mg/kg body weight of nicotine in a single daily dose. Group III: Included 25 rabbits that were exposed to two cigarettes smoke three times per day in a closed chamber. There was a statistically significant difference between the groups as regards the mean longitudinal and transverse diameter of the mitral cells. Treated group III showed lowest mean of longitudinal and transverse diameter of mitral cell. Microscopical examinations showed that there are disruption in the mitral layer and degeneration and disappear of mitral cells in some areas and vacuolated cells in the others, particularly in group III. It was concluded that nicotine exposure and passive cigarette smoking caused reductions in the longitudinal and transverse diameter of mitral cells of the rabbits as well as several histopathological changes, which lead to loss of smell sensation and change in the behavior.