Adrenoleukodystrophy (ALD) is an X-linked peroxisomal disease affecting 1 in 20,000 males either as cerebral ALD in childhood or as adrenomyeloneuropathy (AMN) in adulthood. Recently, the ALD gene has been identified by positional cloning. We report three males patients with AMN and a fourth patient with juvenile ALD. Biochemical studies showed elevated plasma concentration of saturated very-long-chain fatty acids. Genomic DNA of the patients was analysed for possible sequence variations in the ALD gene by PCR amplification and single strand conformation polymorphism analysis. Three missense mutations (Ser515Phe, Glu267Lys and Arg401Trp) and a 9-bp deletion were detected predicting, respectively, the replacement and absence of amino acids in the deduced amino acid sequence of the ALD protein. In the patients' families, detection of the respective mutations allows the identification of carriers of ALD/AMN. Mutational screening in ALD families is of practical importance in improving genetic counseling.