A complete set of diallel crosses between four inbred lines of sunflower has been used to study genetic variability of the following characters: duration of phenological phases, dry matter production in each phase considered, leaf area per plant, seed yield and harvest index. The results obtained indicate that, while the additive genetic component is consistent for the characters collected during the first phases of plant dwelopment, the unfixable component of variation is the major part of genetic variability for the characters collected at the end of the onthogenetic cycle, as seed yield and harvest index. The genetic correlations between seed yield and physiological characters as dry matter production and leaf area, are discussed in relation to the possibilitv of their use in sunflower breeding programs.