In a first experiment, vaginally delivered Day 21 and Caesarean delivered Day 20 and Day 21 rat pups were isolated in the presence of various odorants or no odorant for 1 hr immediately following birth. For Day 20 pups, exposure to novel mint odor resulted in higher mortality during isolation than did exposure to the odor of amnion/placenta. In the preterm pups, whole body corticosterone levels were higher in all isolation treatments than they were immediately following birth. For Day 21 pups, isolation treatments had no effect on corticosterone concentrations, but overall, corticosterone levels were higher following Caesarean section than they were following vaginal delivery. A second experiment replicated the mint odor-induced increase in mortality and revealed a lower activity level in preterm pups exposed to mint odor than in those exposed to the odor of amnion/placenta. Mechanical movement of the pups during exposure eliminated the effects of mint odor on mortality and activity. There was a positive correlation between corticosterone concentrations and pup activity during isolation. These results demonstrate potent influences of seemingly minor changes in early sensory stimulation on the preterm pup. The paradigm might provide a useful animal model for studying the effects of variations in ambient stimulation on premature infants.