The two reduction waves of pyrimidine in acid solutions are studied. They consist of two successive one-electron transfer steps coupled with dimerization of the intermediate. Classic and differential pulse (DP) polarography and cyclic and convolution voltammetry have been used. Analyses of the waves using several theoretical models allow the mechanism of the overall electrochemical process to be inferred. It is concluded that the dimerization is of the radical-radical type and takes place in the reaction layer. The second reduction is slow with a transfer coefficient close to 0.5, indicating control by the electron transfer.