Apolipoprotein E allele 4 (apo E ϵ4) is known to be in genetic disequilibrium with Alzheimer's disease and is associated with an earlier age at onset of dementia. Whether apo E ϵ4 is a specific risk factor for Alzheimer's disease or is a more general susceptibility factor that shifts the age at onset of neurodegenerative diseases to earlier ages is unknown. To test these possibilities, we determined the apolipoprotein E genotypes of subjects with familial or sporadic amyotrophic lateral sclerosis (ALS). ApoE allele frequencies of the the apoE gene of the ALS subjects (n = 170, ϵ2 = 0.071, ϵ3 = 0.771, ϵ4 = 0.159) were found to be comparable to the allele frequencies of the general population. Furthermore, no significant association was observed between the age at onset or the duration of ALS and the inheritance of apoE ϵ4: subjects with at least one copy of ϵ4 (sporadic ALS: n = 15, onset at 57.7 ± 13.9 years; familial ALS: n = 23, onset at 53.6 ± 9.5 years, duration [n = 14] of 2.6 ± 1.6 years) had comparable ages at onset and durations to subjects without ϵ4 (sporadic ALS: n = 28, onset at 53.1 ± 17.0 years; familial ALS: n = 56, onset at 50.8 ± 12.1 years, duration [n = 30] of 1.9 ± 0.8 years). The lack of association of apoE ϵ4 with the age at onset and the duration of ALS suggests that apoE ϵ4 does not have a global effect on the pathogenesis of other neurodegenerative diseases.