Atrial natriuretic peptide (ANP) levels of nasal secretion and blood plasma were measured in 40 patients with chronic nasal conditions and 20 healthy subjects by a sensitive radioimmunoassay. In the healthy subjects, the mean blood ANP level was lower than, but not parallel with, the mean nasal ANP level (p less than 0.05). Among the patients, the blood ANP levels were higher in those with nasal polyposis, atrophic rhinitis and nasal allergy, while lower in simple rhinitis and recurrent epistaxis, than in the control group. Apart from nasal polyposis, all the patients were found to have a lower level of nasal ANP. The conclusion is that the nose may be capable of producing ANP independently from the plasma level. In patients with chronic nasal obstructive disease, the endocrine function of the heart is affected also. The relationship of the plasma and nasal ANP may help to explain some rhinological abnormalities.