This study tested McNeill's theory that the iconic gestures that accompany speech in everyday talk convey critical information in interpersonal communication. Using a structured interview to measure the amount of information respondents receive from clause-length clips depicting aspects of a cartoon story, we discovered that when respondents could see the iconic gestures as well as hear the speech they received significantly more accurate information about those aspects of the original story depicted in the clips than when they just heard the speech. We also discovered that it was only with respect to certain semantic categories, namely, the relative position and the size of objects, that the beneficial effect of gestural communication was significant. We then considered in detail how specific attributes of actions and of objects are communicated via the iconic representation within individual gestures. Lastly, we discuss the implications of these findings for models of human communication in this area.