The effect of enzyme addition to the olive paste on the phenolic composition of virgin olive oil has been studied. The experiments were carried out with both Picual and Arbequina cultivars, using the continuous two-phase extraction system at industrial scale and for three consecutive seasons. Phenolic compounds, in particular orthodiphenols, increased their concentration in oils when enzymes were added to the olive paste before the malaxation stage. Among non-orthodiphenols, the lignans 1-acetoxypinoresinol and pinoresinol slightly increased their concentration. In general, the positive effect of enzymes was more marked for Arbequina than for the Picual cultivar. The peroxide index and "Rancimat" stability of oils were also positively affected when using enzymes. Besides, wash waters from the vertical centrifuge showed a higher concentration of phenolics when the pastes were treated with enzymes. Therefore, the use of enzymatic formulations during the extraction process of olive oil may not only increase the oil yield but also the nutritional quality of the oil. (C) 2001 Elsevier Science Ltd. All rights reserved.