Investigations on the acidic fractions from extracts of a culture of Mycosphaerella rubella led to the isolation of a new unsaturated dihydroxy acid, 6,13-dihydroxytetradeca-2,4,8 trienoic acid, and two of its derivatives, which are probably artifacts. Their structures were determined on the basis of H and C NMR evidence. The absolute configuration of the chiral centres of the new acid was elucidated using the modified Mosher's method.