When isolated from both mother and litter-mates, neonatal rats and mice emit ultrasonic calls. Numerous stimuli elicit ultrasounds from the neonate, including handling, hypothermia, and olfactory and tactile stimulation. Moreover, these vocalizations are affected by drug administrations and changes in social variables. Although it is known that pups' vocalizations elicit a prompt expression of maternal behaviours such as searching and retrieving, the communicative role of infant, ultrasonic vocalizations is still a matter of investigation. A fine analysis of ultrasonic vocalization per se, as well as the study of the different contexts in which calls are emitted, may contribute to a better understanding of their possible role in mother-infant communication. Eight-day-old outbred mice were isolated from the mothers and randomly exposed to four different environmental contexts: 1) low temperature; 2) tactile stimuli; 3) odour from the nest; 4) odour from a conspecific adult male. Vocalizations emitted were recorded and successively analysed. Spectrographic structure of the calls revealed that it ultrasonic calls by young mice are differently shaped and ii) the context under which vocalizations are emitted strongly influences the kind of such calls.