Cold stress leads to increased mortality and morbidity in very low birthweight (VLBW) infants. We have studied temperature stability of VLBW infants in incubators controlled by air (air mode) and baby temperatures (servo mode) using a computer linked monitoring system, which continuously recorded 4 temperatures and humidity from the infant and environment. Thirteen infants (median bw 980 g, gest. 27 weeks) were studied using servo mode and five infants (median bw 1000g gest. 28wks) using air mode. No changes were made in unit policy and the infants were studied while undergoing routine intensive care in the first 4 days of life. Twenty four hour computer graphs showed clearly that the servo mode infants were exposed to wide swings in ambient temperature and to significantly more cold stress than those in air mode. These graphs also highlighted several other problems with the servo control system.The table gives the mean (±SD) daily variance for coretoe temperature difference (ΔT) for the two groups. Infants in such servo mode showed a significantly greater variance of ΔT in the first 2 days, suggesting an increase in cold stress. Infant temperature became more stable with increasing gestational and postnatal ages. VLBW infants undergoing intensive care suffer less cold stress in air mode incubators.