Bovine SH-k-casein (k-C-pool) was fractionated into five components based on carbohydrate and sialic acid contents (k-C-P1 < k-C-P2 < k-C-P3 < k-C-P4 < k-C-P5) by ion-exchange chromatography (DEAE-cellulose). Chymosin susceptibility observed by monitoring changes in optical density during enzyme action, varied among the components. This was a reflection of the difference in self-association of the proteins in aqueous dispersion as determined by hydrophobic interaction chromatograph. There was an inverse relationship between surface hydrophobicity of the protein polymers (k-C-P2 >k-C-P3 >k-C-P4 > k-C-P5 > k-C-P4 > k-C-pool) and their susceptibility to chymosin at 37°C, pH 6.8 (k-C-pool >k-C-P1 >k-C-P5 > k-C-P4 > k-C-P3 > k-C-P2). Mild heating decreased susceptibility and affected flocculation of all except the highly glycosilated components k-C-P4 and k-C-P5 reflecting amphipathicity imparted thermostability.