Histamine, norepinephrine and serotonin were assayed and localized by fluorescence histochemistry in normal mucosa and nasal polyps because of their possible role in the development of inflammation and edema. Histamine was present in greater concentration in nasal polyps than in normal mucosa. Norepinephrine was present primarily in the base of nasal polyps and in greater concentration than in normal mucosa. Patients with aspirin sensitivity and asthma had much lower histamine concentrations in their nasal polyps than all other patients with nasal polyps. A proposal for a possible mechanism of formation of nasal polyps based on vascular and inflammatory mechanisms and incorporative roles for histamine and norepinephrine is presented.