X-linked adrenoleukodystrophy/adrenomyeloneuropathy presents a wide variation of clinical manifestations and may mimic several diseases. A screening investigation by measuring plasma saturated very long-chain fatty acids was performed in two groups of patients. Among six patients with hereditary spastic paraparesis one woman was detected to be a heterozygous gene carrier. However, in a group of eleven adult men with idiopathic Addison's disease the plasma concentrations of very long-chain fatty acids were all within normal limits. We conclude that X-linked adrenoleukodystrophy and symptomatic heterozygous females should be considered in cases of progressive spastic paraparesis.