Disulfide-reduced and carboxymethylated ovalbumin was treated at pH 9.9 and 55 degrees C for 24 h as a specific condition for preparation of S-ovalbumin. The stability and conformation of the product were investigated. Such alkaline treatment converted native protein to S-ovalbumin, but this modified ovalbumin was not stabilized, according to results of calorimetric analysis. Instead, it had lost its native like conformation; the magnitude of CD spectra decreased. The conformation after alkaline treatment was not clear, but the possibility of aggregation was excluded by electrophoretic analysis. These observations showed that the transformation of native ovalbumin into S-ovalbumin requires the presence of the disulfide bond.