Alzheimer's dementia (AD) is a progressive neurodegenerative disease which is one of the most common forms of dementia in the above 65 years old age group. Diagnosis is based upon evaluation of cognitive skills, elimination of other dementia associated diseases and on cranial CT examination. However, definitive diagnosis is proved only by neurohistological findings. The etiology of the disease is unknown and effective treatment is not available. Intensive research into the pathomechanism of the disease revealed a connection between increased frequency of apolipoprotein E4 allele and later onset of AD. The aim of the author's research was to characterize apolipoprotein E polymorphisms in AD patients and to examine immunological factors which could play an important role in the development of the disease such as the polymorphism of complement and lipoprotein(a) [Lp(a)] alleles previously had not been investigated. 35 AD patients (26 female, 9 male) were examined (mean age 66.4 years +/- 8.7 SD). 18 of these patients showed late onset of the disease. The E4 allele was significantly more frequent in both early and late onset groups compared to controls (0.29 vs. 0.14 and 0.33 vs 0.09). The high frequency of apo E4 found in the early onset group in this study differs from other international data. Serum lipid, lipoproteins, Lp(a) concentrations and Lp(a) phenotype distribution showed no significant difference compared to controls. Furthermore, it was found that the frequency of complement C4AQ0 (null) and Bf F alleles was higher in the late onset AD group compared to controls (0.35 vs 0.139 and 0.305 vs. 0.225) suggesting an active involvement of the complement system in the pathogenesis of this disease.