The Pervenets mutation raises the oleic acid content (OAC) from about 25% (LO linoleic sunflower) to over 75% (HO sunflower) in sunflower seed oil whatever the genetic backgrounds of the genotypes: fixed mutant lines, hybrid between fixed mutant lines and, surprisingly, both direction cross hybrids between high oleic × linoleic and linoleic × high oleic lines. Here we develop the methodology to point out the coincidence between the mutation and the oleate-desaturase locus. The mutation function is modeled to explain the phenotype. A series of sunflower genotypes developing embryos between 12 and 24 days after pollination without or carrying the Pervenets mutation was used to compare oleate-desaturase transcript accumulation. This revealed the presence and absence of the transcript, in normal LO and Pervenets HO embryos, respectively, whereas stearate-desaturase transcript accumulation was equivalent in both types. The RFLP approach using oleate-desaturase cDNA as a probe has revealed that in comparison with the linoleic sunflower, those carrying Pervenets mutation displayed, besides a common 5.8 kb EcoRI fragment, an extra 8 kb EcoRI fragment and, with HindIII, the shift from 8 kb to 16 kb of a HindIII fragment. The common 5.8 kb EcoRI fragment to Pervenets and nor mal sunflower carries an oleate-desaturase gene. The insertion unique to the sunflower carrying Pervenets mutation has to carry oleate-desaturase sequences. The genetic studies of this mutation have lead to contradictory results in the inheritance pattern of the HO trait due to variable mutation expression and several genetic factors affecting the HO level. Thus, it appeared important to study the inheritance in a set of recombinant inbred lines. Moreo ver, we pointed out that the presence of the mutation is not sufficient to induce the HO phenotype since a suppressor of the mutation “supole” may mask the HO trait. The supole allele is revealed in half of the HO RI lines, and consequently its accurate mapping is difficult. Thus conjunction of the molecular and genetic methods and of material construction was required to solve this problem and to provide efficient tools to breed HO sunflower.