The relevance of the apolipoprotein E epsilon 4 allele as risk factor for Alzheimer's disease is independent of age. This was demonstrated in 126 patients and 72 healthy controls. The age in both groups varied between 44 and 95 years. An earlier onset of symptoms among carriers of the epsilon 4 allele, however, was observed only in the oldest patients. This may reflect a selection bias which is due to the association of the epsilon 4 allele with two competitive age-dependent risks: for Alzheimer's disease and for coronary heart disease. In a subsample of 64 patients who had participated in a longitudinal study no relationship was found between the apolipoprotein E genotype and clinical symptoms or symptom progression.