Apolipoprotein E (APOE) genotypes and cerebrospinal fluid (CSF) tau protein concentration were evaluated in patients suffering from semantic dementia, with the aim of determining whether these markers could help to differentiate this condition from Alzheimer's disease (AD) in early stages. By strictly following diagnostic criteria for semantic dementia, we found a clinically homogeneous group comprising eight patients from a total population of 621 subjects referred for dementia investigation. CSF tau protein concentrations were moderately increased with a small intraindividual variation 437+/-36 pg/ml (mean+/-SD) compared to healthy control individuals. APOE genotype distribution showed an over representation of the epsilon4 allele (69% epsilon3, 31% epsilon4 and no epsilon2), a pattern similar to that found in AD. These results indicate that semantic dementia is a rather uncommon but clinically distinct condition which shows a moderate increase of CSF tau protein levels and for which the epsilon4 allele is a risk factor.