Changes in the human neonate's activity and respiration following olfactory stimulation are reported. Results of 2 experiments demonstrate that (a) the neonate does respond to such stimulation and in different degrees to acetic acid, asafoetida, phenylethyl alcohol, and anise oil; and (b) there is adaptation with repeated stimulation by asafoetida and anise oil, and recovery of response following a temporal delay. Order of presentation of odors also affects the occurrence of response. No clear differences were obtained between so-called pleasant and unpleasant odors. Alternative interpretations are suggested for the adaptation effect and response differences between odors. Response differentiation, or increased refinement of response with increased practice, was observed to occur. (PsycINFO Database Record (c) 2006 APA, all rights reserved)