It is generally said that falling intonation is used at the end of a declarative sentence. However, this is not the case with all stretches of spontaneous speech which are marked in transcription as sentences. The present paper examines intonation patterns appearing at the end of declarative sentences in oral presentations, and discusses instances where falling intonation does not appear. The texts used for analysis are eight oral presentations collected at international conferences in the field of physics. Quantitative and qualitative analyses are carried out. Three major factors related to discourse structure have been found for non-occurrence of falling intonation at sentence boundaries.