AbstractThe authors have devised a new, simple method for the diagnosis of adrenoleukodystrophy (ALD) using a dried blood spot sample. Fatty acid from the dried blood spot was extracted and methylated with HCl‐methanol. Fatty acid methyl esters were analyzed by gas chromatography‐mass spectrometry. Fatty acid composition of the blood spot from five patients with ALD and from five healthy controls was determined from the mass chromatogram of the m/z 143 ion, [(CH2)6COOCH3]±. The ratios of tetracosanoic acid to docosanoic acid (C24:0/C22:0) and of hexacosanoic acid to docosanoic acid (C26:0/C22:0) were significantly greater in ALD patients than in controls. The C24:0/C22:0 ratios of ALD patients and of controls were 2.08 ± 0.33 and 1.47 ± 0.16 (mean ± SD), respectively. The C26:0/C22:0 ratios of ALD patients and of controls were 0.31 ± 0.024 and 0.092 ± 0.041, respectively. The fatty acid composition of the dried blood spot did not change at room temperature within a week. Since the specimens can be sent by mail, this method could be applied to the screening of other “peroxisomal” diseases, such as neonatal ALD and Zellweger synd