Adrenoleukodystrophy is an X-linked severe demyelinating disease with pathognomonic accumulation of saturated very long-chain fatty acids (VLCFA) in tissues and body fluids in affected males. The identification of women heterozygotes is also based on increased serum VLCFA concentrations. We describe the results of measuring serum VLCFA concentrations in 59 females of various ages with heightened risk of carrier status. In female carriers aged 22-50 years we found serum VLCFA concentrations in a range characteristic of heterozygotes; VLCFA levels were normal in female carriers aged 55-64 years. In women aged 37-50 years in whom repeat studies of VLCFA concentration were performed after 5 years, a reduction in VLCFA was observed. The results we obtained point to a reduction of serum VLCFA concentrations as X-ALD heterozygotes age.