The hydrolytic stability of ribose phosphodiester bond within several types of oligonucleotides was measured at 150-200 degreesC using a real-time monitoring method. It was observed that the stability of a phosphodiester linkage is dependent on the surrounding sequences of the phosphodiester linkage at high temperatures, The fact indicates that some weak interactions, such as hydrophobic interaction, might be effective within the oligonucleotides at high temperatures.