The epsilon4 allele of apolipoprotein E (apoE) is found more commonly among patients with Alzheimer's disease (AD) than in the normal population. ApoE is associated with brain amyloid, a component of cerebral amyloid angiopathy (CAA), which is both a pathological feature of AD and a frequent cause of lobar intracerebral hemorrhage (ICH). We hypothesized that the frequency of epsilon4 allele is higher in patients with CAA-related ICH than in hypertensive ICH and in the normal population. To test this hypothesis we compared the frequency of apoE alleles in four populations: 24 patients with lobar ICH, 24 matched patients with hypertensive ICH, 24 matched normal controls, and 173 population controls. Although there was a tendency to a higher frequency of apoE epsilon4 in lobar ICH patients, we found no significant differences in the frequency of this allele between the four studied populations. In addition we did not confirm the finding of some authors of a higher frequency of apoE epsilon2 in patients with lobar ICH than in the normal population. Previous studies on the subject are discussed. The relationship between apoE polymorphism and lobar CAA-related ICH remains to be clearly defined.