Recent trends in research on intonation have suggested that it is a universal feature with basis in physiology, neurology, and evolution. This paper addresses intonation in Mandarin Chinese as a specific case using acoustic data collected from natural discourse situations. The parameters of duration, fundamental frequency, amplitude, and pitch range are analyzed, and the relationship between stress and rhythm is explored. This study finds that intonation affects all parts of an utterance, and that lexical tones are modified substantially under different situations and states. Stress operates under the Principle of Disequilibrium by disrupting the normal rhythmic hierarchy. The expression of finality or definiteness is often associated with falling tone contours while hesitation and continuation are often characterized by raised and lengthened contours. It is proposed that intonation is an essential component of meaning, and that attitudes and emotions are crucial determinants of prosody.