Five patients with various clinical and genetic phenotypes of adrenoleukodystrophy were treated with a diet enriched with glycerol trioleate and glycerol trierucate (GTE). In all patients platelet counts decreased upon the administration of GTE, but no bleeding symptoms occurred in any of the patients, and bleeding time remained normal. Pseudothrombocytopenia was excluded in all patients. Thrombocytopenia was marked (84,000-37,000/mm) in three of the patients but was fully reversible after discontinuation of GTE. Mean platelet volumes were abnormally increased in all patients. When GTE was again administered by stepwise increasing the daily dose, platelet counts showed a clearly dose-dependent decrease. Bone marrow biopsies revealed no evidence of reduced megakaryocytopoiesis. The data indicate that in patients with adrenoleukodystrophy treated with GTE platelet counts should be closely monitored because thrombocytopenia may limit the maximal daily intake of GTE.