This paper describes the declination trends of f0 in conversational speech data. A 10-minute dialogue interaction from a corpus of spontaneous speech was annotated to identify inter-silence units (ISU) and turns. Detailed annotation of the ISUs was conducted in terms of communicative types and pitch patterns. f0 declination was measured by (1) fitting a regression line to f0 trajectories and (2) by fitting additional regression lines to the data points below and above the original (central) regression line. The slope of declination as well as the height of ISU/turn-initial f0 peak were examined as a function of the duration of the ISU or turn. The results suggest that declination is indeed present in conversational speech data, at the level of both the ISU and the turn (73% of the analysed ISUs exhibited negative f0 declination slope). There is a tendency for the steepness of the slope to decrease and the height of IS-turn-initial f0 peak to increase as the duration of the ISU or turn increases. The results are discussed in the context of Projection and Reaction theories and of Hard vs. Soft preplanning of speech production. The findings are of potential interest for the development of human-machine dialogue systems.