We report the biochemical and clinical results obtained during a dietary erucic acid (C22:1) therapy in 20 patients affected by X-linked adrenoleukodystrophy (ALD). Six patients were very severely affected, 9 had milder neurological symptoms and 5 were presymptomatic. Mean basal levels of plasma C26:0 were 1.41 +/- 0.48 micrograms/ml in ALD patients (control values: 0.33 +/- 0.12). In all patients C26:0 decreased to virtually normal values. In spite of good biochemical response and absence of consistent side effects of therapy, no encouraging data were observed during the clinical follow-up. The presymptomatic subjects were still free of symptoms after more than 1 year of therapy. The symptomatic patients, however worsened or did not show any improvement.