In 43 patients with cystic fibrosis (age 8-23 yr, 26 boys and 17 girls) attending a summer camp in a mountain rehabilitation center and in 25 parents (heterozygotes) plasma epinephrine, norepinephrine, dopamine and plasma activity of dopamine-β-hydroxylase were determined as well as the 24-h excretion of the free urinary amines (epinephrine, norepinephrine, dopamine), their Omethylated products (metanephrine, normetanephrine, 3-methoxytyramine) and the urinary phenolic acids (vanilmandelic and homovanillic). Also the metabolic breakdown product of serotonin in urine, the 5-hydroxyindoleacetic acid, was determined. Significantly elevated plasma dopamine (0.03–0.45 nmol/liter for controlsversus1.70–2.21 nmol/liter for cystic fibrosis) and slightly higher plasma norepinephrine levels were found in patients with cystic fibrosis. An increased 5-hydroxyindoleacetic acid excretion was noticed in adolescent patients which correlated with the disease state and the extent of lung involvement. No abnormalities of plasma amine levels were seen in the parents of the patients. Despite controversial results, CF patients seem to have an alteration in catecholamine metabolism which is reflected in higher plasma dopamine levels.