The mode of neocarzinostatin-chromophore (NCS-chr) - apo-neocarzinostatin (apo-NCS) interaction in neocarzinostatin (NCS) complex has been described. The NCS-chr release from the NCS complex in the presence of various reagents, which destroy the highorder structure of the protein under various pH conditions, was examined. We found that (i) sodium dodecylsulfate, Nonidet P 40, 8 m urea, and 2-propanol did release NCS-chr from NCS, (ii) no NCS-chr release is detected below pH 7, but it is enhanced at high pH and (iii) β-naphthol as a model of naphthalenecarboxylic acid derivative and D-galactosamine as a model of N-methylfucosamine of NCS-chr did release NCS-chr from NCS. These observations indicate that the binding of NCS-chr to apo-NCS may be due to not only ionic interaction between the acidic side chain of apo-NCS and the basic center of an aminosugar moiety of NCS-chr but also hydrophobic interaction between the hydrophobic amino acids of apo-NCS and hydrophobic moieties of NCS-chr. Apo-NCS is a very hydrophilic protein, since it has an high hydrophilic amino acid content. So, local hydrophobicity, local hydrophilicity and secondary structure of apo-NCS were predicted. Hydrophobic residues of apo-NCS predominantly located in β-sheet structures near the carboxyl-terminus. These predictions are in good agreement with the results suggesting that NCS-chr bound carboxyl-terminal-43-peptide of apo-NCS in our previous result.