Nasal polyps are a condition of uncertain aetiology but are associated with diseases of the lower respiratory tract, in particular, asthma and cystic fibrosis. Asthma may be mediated by mastcell reactions and the commonest allergen to degranulate mast cells is house dust mite. Mast cells have been shown to be degranulated in nasal polyps. This study looks at thirty-six patients who had nasal polypectomy and of whom fourteen were asthmatic to see if histamine wasreleased from polyp tissue and peripheral blood when they were challenged with antihuman IgE and extracts of house dust mite and mixed grass pollens. These results were compared with skin tests to these allergens. A release of above 15 per cent of the total histamine was considered positive. Eight patients released histamine from polyp tissue but only three patients released histamine with both anti IgE and allergen extracts. The release from blood compared well with positive skin tests (p >0.05 corrected chi square). Although allergy may cause mast cell degranulation in polyp tissue, this study suggests that it is unlikely to be a common cause of nasal polyps.