Urea, ammonium, arginine and ornithine contents after fermentation and biological aging of wine for two Saccharomyces cerevisiae strains with different O-2 levels were analysed. Yeast growth and the excretion or uptake of urea were both dependent on yeast strain and the fermentation conditions. Based on these results, flor yeasts can metabolize the urea produced during fermentation in the event of arginine being depleted in the process. However, if any arginine remains after fermentation, then the urea concentration increases during the veil formation period.