Thirty-seven patients with clinically diagnosed infantile seborrhoeic dermatitis (ISD) were studied in an attempt to establish the significance of transepidermal water loss (TEWL) and water content in the stratum corneum, in active disease and after recovery. All the patients were treated daily with topically applied borage oil (containing 24% gamma-linolenic acid). With this regimen they were completely free from all skin symptoms within 3-4 weeks. Analyses of essential fatty acids in serum showed aberrations as previously described, with elevated levels of 18:1w9 and 20:2w6. TEWL and water content were recorded at the time of diagnosis and after treatment from the right forearm in skin that was free from symptoms and not treated with borage oil. Twenty-five healthy children in an age-matched group without skin disorders were used as controls. Significant differences in TEWL between patients and controls were found before treatment. After treatment no significant differences were found. There were no significant differences between controls and patients regarding water content in the stratum corneum. Gamma-linolenic acid is suggested to be of importance in maintaining normal TEWL and also in promoting recovery in patients suffering from ISD.