BACKGROUND: The determination of apo E polymorphism through the phenotyping is not suitable for large studies in the clinical laboratories because of various problems. So apo E genotyping has been developed. We present a method of apo E genotyping using a modified amplification refractory mutation system(ARMS) technique. METHODS: We used four primers to detect the region containing two mutation points coding amino acid residues 112 and 158 and have developed a method of apo E genotyping by the modified ARMS technique. Apo E genotyping were performed by both the modified ARMS technique and the INNO-LiPA Apo E kit(Innogenetics, Belgium) with the following frequency distribution: Epsilon2/2(n=10), Epsilon3/3(n=15), Epsilon4/4(n=7), Epsilon2/3(n=9), Epsilon2/4(n=12), Epsilon3/4(n=13). RESULTS: All the samples gave the correct and clear amplification patterns. Modified ARMS correctly distinguished among the six apo E genotypes. The apo E genotypes determined by both methods for every specimen studied were in complete agreement. CONCLUSIONS: This modified ARMS technique involved only two stages: PCR and agarose gel electrophoresis. Since apo E genotyping by the modified ARMS is reliable, simple to perform, less time consuming, and not expensive, we conclude that it is suitable for large sample studies in the clinical laboratories.