The denaturation s processes kinetics of sunflower and cucumber of different genotypes DNA was studied. The thermal denaturation of DNA macromolecules have proved high melting temperatures at sunflower hybrids, in compa-rison with cucumber genotypes, this fact denotes the increased stability of DNA macromolecules. The level of hetero-geneity has varied in dependence of genotype and it has correlated with the highest values of morphological and physio-logical parameters which determines the effect of hybrid vigor in studies of genotypes. The kinetics of denaturation processes, realized on two cucumber families, has proved that the first generation hybrids DNA macromolecules had the melting temperature higher, an increased content of G-C and a higher level of heterogeneity, in comparison with parental lines.