AbstractRecent interpretations of ultrasonic signaling by infant and adult rodents have emphasized the quality of the eliciting stimuli and acoustical parameters of the vocalizations. Infant calls have been hypothesized as being of 2 types: coldelicited and tactually elicited. Adult calls have been hypothesized as reflecting 2 distinct messages: aggressiveness and submission. These interpretations lack an adequate empirical foundation. Further, they suppose a capability of encoding and decoding vocal information by rodents for which no empirically established basis exists. An alternative explanation of both infantile and adult ultrasounds is offered. The proposed model hypothesizes that these vocalizations reflect a state of arousal and that they produce a similar state in nearby animals.