Sclerotinia spp. can attack most parts of the sunflower plant, including capitula and leaves. The different levels of partial resistance shown by a range of hybrids were determined by the rate of growth of Sclerotinia mycelium on plant parts. Even though Sclerotinia isolates varied greatly in agressivity, a similar ranking of the sunflower genotypes according to their resistance to mycelial growth was obtained with all isolates. HPLC analysis of soluble phenolic compounds present in healthy or infected capitula and leaves showed the presence of 25 different compounds in capitula and 19 in leaves. Total phenol content in leaves was much greater than that in capitula; both varied considerably between genotypes. In the two tissues, Sclerotinia infection stimulated the accumulation of existing phenolic compounds to different extents according to genotype. Relations between resistance level and phenol accumulation were tissue specific. In capitula, total phenol content was correlated with resistance, whereas in leaves, the best marker of resistance was the amount of compound 9. It is suggested that phenolic compounds in healthy sunflower plants could be used as markers of Sclerotinia resistance.