When separated from the mother during the first week of postnatal life, young mice and rats emit ultrasonic vocalizations. Changes in the rate of vocalization have been extensively reported as a function of age, temperature, olfactory and tactile stimuli as well as a consequence of social variables or drug administration. In the recent controversy concerning the interpretation of ultrasonic vocalization as distress signals, the hypothesis has been advanced that ultrasounds could merely be "an acoustic byproduct" of laryngeal braking serving thermogenesis. Though a large body of evidence has shown that thermal cues modulate ultrasonic vocalization, it appears that they cannot account for the major features of the vocal response of young rodents. In order to investigate the possible communicative function of ultrasonic emission in neonatal rodents, 8-day-old mice were videorecorded and their behaviour correlated with the display of ultrasonic vocalization by a slow motion analysis. Vocalization emission appears to be higher during both locomotion and periods closely related with head rising behaviour. Studies involving sonographic analysis are in progress to evaluate it developmental pattern of behaviours associated with vocalizations, ii) differences in behaviour associated with changes in acoustic parameters and iii) differences in the structure of the calls as a function of the context m which vocalizations are emitted (i.e. alteration of ultrasonic output induced by changes in the olfactory context).