This study assessed the relative efficiency of different warming devices (surgical sheets covering the body and a tubegauze on the head, forced-air warming, warming mattress) commonly used to prevent body hypothermia during neonatal surgery. Dry heat losses were measured from a thermal manikin, which simulated a low-birth-weight neonate of 1,800 g. The manikin's surface temperatures (35.8 degrees C) corresponded to those of neonates nursed in closed incubators. Experiments were performed in a climatic chamber at an ambient temperature of 30 degrees C, as commonly found in operating theatres. The supine manikin was naked or covered with operative sheets with a 5x5 cm aperture over the abdomen. Its head could be covered by a tube-gauze. Additional warming was provided by conduction through a warming mattress (surface temperature, 39 degrees C) and/or by convection (Bair Hugger, forced-air temperature 38 degrees C). Covering the manikin with surgical sheets decreased the dry heat loss by 10.4 W. Additional forced-air warming was more efficient than the warming mattress to reduce the total dry heat loss (6.8 W vs 2.1 W). Heat losses were reduced by 7.9 W when combining the warming mattress and Bair Hugger. The heat loss from the head of the covered manikin was reduced from 4.5 W to 3.9 W when the head was covered with the tubegauze. Our data indicate that forced-air warming is more effective than conductive warming in preventing neonatal hypothermia during abdominal operations.