A bacterial strain isolated from soil and identified as a Bacillus species produced two endo-beta-N-acetylglucosaminidases in the culture broth when it was cultivated on medium containing only hen ovomucoid. Almost no production of the enzymes occurred when the bacterium was grown on glucose medium. The two endo-beta-N-acetylglucosaminidases, named Endo-BI and Endo-BII, were separated and purified to homogeneity by preparative gel electrophoresis after partial purification by column chromatography on DEAE-resins. Endo-BI hydrolysed oligosaccharides of both hen ovalbumin and ovomucoid. In contrast, Endo-BII could act only on oligosaccharides of hen ovalbumin and showed almost no activity towards those of hen ovomucoid. Deglycosylation of hen ovomucoid was performed with the partly purified endo-beta-N-acetylglucosaminidase preparation, with the aid of contaminating beta-N-acetylhexosaminidase. The deglycosylated ovomucoid exhibited no changes in trypsin inhibitory activity but was very unstable to heat treatment in comparison with native ovomucoid. These results suggest that oligosaccharides of ovomucoid have an important role in the stabilization of the protein against heat.