The nasal cavity has been described as the portal of entry to the respiratory tract and is constantly exposed to airborne pollutants. The nasal cavity is susceptible to chemically induced injury as a result of exposure to inhaled irritants. Inhalation pathology concerns the lesions present in the tissues of the upper respiratory system. These include the larynx, nasal turbinates, trachea, tracheal bifurcation, and associated lymph nodes. Rats, mice, dogs and non-human primates are commonly used in inhalation studies. Following an overview of an inhalation study, the collection and processing of tissues, the cutting of the slides and the major nasal histology and pathology of the above species will be discussed. Examples of common lesions observed in inhalation studies e.g., arytenoid epithelial hyperplasia, ventral cartilage necrosis, respiratory and olfactory epithelial damage, increased goblet cells, reduced nasal associated lymphoid tissue and tumours will be demonstrated. Taken together, this paper aims to represent a compilation of the current knowledge relative to the normal structure of the upper respiratory system of rats, mice, dogs and non-human primates with a comprehensive characterisation of toxic and proliferative lesions.