The mechanism of the renaturation of DNA molecules is examined on the basis of the bimolecular interaction of Gaussian chain polymers. In the nucleus formation by hydrogen bonding in segment-segment interaction, two types of interchain interaction, that is, one between complementary chains and one between noncomplementary chains, and one noncomplementary intrachain interaction are considered to be in competition. Several previously observed characteristics of the renaturation process are displayed by this simple model. I n particular it accounts for the dependence of the extent of renaturation on the heterogeneity, molecular weight, and radius of gyration of DNA, and of the ratios of the reaction rates between complementary and noncomplementary segments. Among these variables the ratio of reaction rates has shown to have a quite specific value, aa high as the order of lo4, which favors the complementarystrand interaction. This very great bias in favor of complementary strand interaction emphasizes that the renaturation phenomena displays the same character of biological specificity that is associated with enzymesubstrate interaction or antigen-antibody interaction. Moreover, since DNA is a good example of a one-dimensional system, it seems to provide a suitable clue for pursuing the analysis of pattern recognition a t the macromolecular level.