Sixteen unselected patients with nasal polyps had the levels of substance P and IgE decapeptide measured by ELISA in the oedema fluids and their matched sera. All 16 samples had low levels of substance P in their sera and had high level of substance P in eight samples of nasal polyp oedema. There was a considerable variation in the values of IgE decapeptide found in the sera but 14 polyp oedema fluids had high levels of IgE decapeptide. This study supports the idea that there is a linkage between the cellular and neurovascular responses. High levels of IgE decapeptide suggest that mast cell reactions occur in the majority of cases and that IgE may be implicated in the process of mast cell degranulation.