Twenty-one pre-adolescent cystic fibrosis (CF) children with good clinical scores had significant (P less than 0.001) deficiencies of arachidonic (mean 3.8% of total plasma fatty acids +/- SD 1.4) and linoleic (18.1 +/- 6.3) acids compared with controls (6.0 +/- 1.0, and 27.6 +/- 3.9, respectively). Despite the presence of pulmonary involvement of varying severity in all the CF children, neither arachidonic nor linoleic acid levels correlated significantly with pulmonary function measured by spirometry. All children had adequate caloric and fat intakes, and the coefficient of fat absorption correlated with none of the deficient fatty acid levels. These findings suggest that deficiencies of arachidonic and linoleic acids are of minor importance in the early development of pulmonary involvement in CF, and that factors other than fat malabsorption and decreased dietary intake probably contribute to fatty acid deficiency.