Aldosterone was measured in the saliva of 20 patients with cystic fibrosis and a group of 20 normal children matched for age and sex. Mean levels were higher in the patient group but overall differences were small and statistically not significant. For the first time a link between aldosterone level and disease severity in patients with cystic fibrosis was established using a simple scoring system to assess disease activity. Urinary and salivary electrolytes were similar in the two groups. The results do not support the proposed hypothesis that the salivary glands of patients with cystic fibrosis are insensitive to aldosterone.