OBJECTIVE: This study evaluated peripheral vasoconstriction in extremely low birth weight (ELBW) infants when body temperature decreased during the first 12 h of life. STUDY DESIGN: An exploratory, within-subjects design with 10 ELBW infants. Abdominal and foot temperatures were measured every minute. Peripheral vasoconstriction (abdominal>peripheral temperature by 2 degrees C) and abdominal-peripheral temperature difference were also evaluated. RESULTS: Abdominal and peripheral temperatures were significantly correlated within each infant. One 880 g infant exhibited isolated peripheral vasoconstriction; a 960-g infant had abdominal temperatures >1 degrees C higher than peripheral temperatures. Eight smaller infants exhibited no peripheral vasoconstriction and spent most of their observations with peripheral greater than abdominal temperatures. In eight infants, mean temperature difference was significantly higher when abdominal temperature was <36.5 degrees C. CONCLUSION: Most ELBW infants did not exhibit peripheral vasoconstriction during their first 12 h of life, despite low temperatures. ELBW infants' vasomotor control may be immature during this period.