A method of genotyping single nucleotide polymorphisms ("SNP") and point mutations in nucleic acid based on chain extension by polymerase. This invention is based on the fact that the nucleoside immediately 5 adjacent to any SNP/point mutation site is known, and the neighboring sequence immediately 3 adjacent to the site is also known. A primer complementary to the sequence directly adjacent to the SNP on the 3 side in a target polynucleotide is used for chain elongation. The polymerase reaction mixture contains one chain-terminating nucleotide having a base complementary to the nucleotide directly adjacent to the SNP on the 5 side in the target polynucleotide. An additional dNTP may be added to produce a primer with the maximum of a two-base extension. The resultant elongation/termination reaction products are analyzed for the length of chain extension of the primer, or for the amount of label incorporation from a labeled form of the terminator nucleotide.