An eye tracking methodology was used to evaluate 3- and 4-year-old children's sensitivity to speaker affect when resolving referential ambiguity. Children were presented with pictures of three objects on a screen (including two referents of the same kind, e.g., an intact doll and a broken doll, and one distracter item), paired with a prerecorded referentially ambiguous instruction (e.g., "Look at the doll"). The intonation of the instruction varied in terms of the speaker's vocal affect: positive-sounding, negative-sounding, or neutral. Analyses of eye gaze patterns indicated that 4-year-olds, but not 3-year-olds, were more likely to look to the referent whose state matched the speaker's vocal affect as the noun was heard (e.g., looked more often to the broken doll referent in the negative affect condition). These findings indicate that 4-year-olds can use speaker affect to help identify referential mappings during on-line comprehension. (Contains 4 figures and 1 table.)