Patients with allergic and non-allergic nasal disorders may complain of symptoms of itching, discharge, congestion or fullness, and obstruction of airflow. The actions of sensory nerves and parasympathetic reflexes are central to the development of these symptoms, and likely play crucial roles in allergic and non-allergic nasal pathology. Nasal provocation studies have provided much information about the nature of the processes which contribute to the production of nasal secretions and the development of obstruction to nasal air flow. The results of human nasal provocation studies will be discussed after a review of the special anatomy of the human nasal mucosa, its vasculature, and its innervation.