This study examined the relationship between assertiveness and such physiological features as heart rate and vocal inflections(pitch and intensity). The vocal data were assessed from a first person simulation in which participants interacted with video-based characters. During the simulation, the participants' partner (friend, family member, or acquaintance) completed inventories that asked their perceptions of the participant's assertiveness and aggressiveness for the scenes. Results found heart rate and mean intensity of speech were unique indicators of peer-rated aggressiveness. Also, standard deviation in pitch and heart rate accounted for unique variance in peer-rated assertiveness. The results suggest that physiological and verbal measures may be a useful means of distinguishing between assertiveness and aggressiveness of team members.