Tetra-primer amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) is a new efficient method for single-nucleotide polymorphism (SNP) genotyping. To determine the optimal conditions for ARMS-PCR we attempted to genotype ten SNPs. DNA was extracted from the peripheral blood of 168 unrelated healthy Japanese volunteers. Two problems inhibited uniform efficiency of the amplification of three bands. The first problem was the lower amplification efficiency of the shorter and allele-specific products compared with the largest product. This phenomenon was overcome by increasing the relative concentration of the inner primers. The second problem was non-specific amplification of the shorter products. To reduce the amplification of these non-specific bands, adjusting any one of the following PCR conditions was effective: i) reducing the ratio of the inner primer concentration relative to that of the outer primers; ii) increasing the annealing temperature for the initial 5-10 cycles; iii) hot start PCR. With these procedures all ten of the SNPs were successfully genotyped. Our present data may be useful in the further application of tetra-primer ARMS-PCR to SNP genotyping.