1. The antioxidant effects of the water-soluble fraction of baked sponge cakes made with silky fowl eggs and White Leghorn eggs were studied. The mechanism of the antioxidant effect was also investigated. 2. The antioxidant effect on the oxidation of linoleic acid increased in the water-soluble fraction of cake made with silky eggs. In contrast, Leghorn eggs significantly decreased the rate of antioxidant activity. The browning index of the water-soluble fraction of baked sponge cake made with silky fowl eggs changed from 0.052 to 1.240 after 20 min at 180 degrees C, while that made with Leghorn eggs changed from 0.037 to 0.710. 3. There are correlations between the rate of browning index and antioxidant activity. Superoxide anion (O2(-)) and hydrogen peroxide (H(2)O(2)) in water-soluble fractions of baked sponge cakes made with silky fowl eggs and hen's eggs were formed during light exposure for 20 min at 10,000 lux, and their formation could be significantly inhibited by the addition of tryptophan or mannitol, scavengers of hydroxyl radicals (*OH). These results were strong evidence of direct participation of *OH, formed by the Haber-Weiss reaction, in the water-soluble fraction of baked sponge cakes. The rate of decrease in active oxygen by scavengers decreased in Leghorn eggs more efficiently than in silky eggs. 4. The present experiments suggested that the use of silky fowl eggs could improve the quality and oxidative stability of baked cakes.