Work on clear versus conversational speech has shown that speakers expand the vowel space in clear speech, which maximizes the perceptual contrast, making it easier for listeners to parse the speech signal. This study investigates how the realization of lexical tones changes for different speech tasks, and whether it is sensitive to the number of repetitions of the same word in a conversation. Native Mandarin speakers participated in a map task in which they were instructed to explain the route on the map to a partner. The first and last tokens of each target word were extracted from the dialogues and compared to the same word read from a list. Pitch and duration were normalized and quadratic curve fitting was performed on the test items. Results of statistical analyses show that contour tones from later occurrences of the target words have a smaller slope, are more linear, and tend to have pitch values closer to the overall average pitch of the speaker. In other words, all tones are realized closer to a midlevel tone when they have been previously mentioned in the conversation. In this sense, there is a contraction of the tone space for later tokens.