The activation of oxygen stress-related enzymes was compared in regenerating and non-regenerating tulip bulb scale explants and regenerating stalk explants. The phospholipid composition of scale explants showed an increase of linolenic acid (1-15%) and a decrease in linoleic acid (70-55%). After incubation it was comparable to that of stalk explants in which no changes were observed. In all tested systems an increase in activity of catalase, peroxidase, SOD, lipoxygenase, polyphenoloxidase and phenylalanine ammonia lyase, was observed during incubation of the explants. The reaction can be divided into two phases. The first one (observed for scale explant lipoxygenase and to a lesser extent for SOD) occurs rapidly (1-2 h) after cutting the explants and appears to be wounding related. In the second phase (observed for all enzymes), starting during the first week of incubation, wound healing and regeneration can be observed. The activation of catalase, peroxidase and phenylalanine ammonia lyase was comparable in all tested systems and appears not to be related with the differences in tissue culture performance. In the second phase, the activity of lipoxygenase, peroxidase, catalase and phenylalanine ammonia lyase decreases in regenerating explants, while in non-regenerating explants they remain high. Our conclusion from these results is that oxidative damage is not the prime cause of the low regenerability of tulip bulb scale explants.