['Temperature control is essential during pediatric surgery. The effectiveness of two methods of warming intravenous (i.v.) fluids to preserve normothermia was compared during abdominal surgery.', 'Intraoperative core temperature (CT) was measured in 59 children, 8 years of age and younger. Patients were randomly allocated to two study groups according to the method of fluids warming. In Group M (n = 30), fluids were warmed by placing the i.v. tubing under a warming mattress, and in Group T (n = 29), by using an active i.v. fluid tube warming system. Observations of CT, infusion fluid temperature (IFT) at the entry to the patient and other relevant parameters were made at 30-min intervals throughout the surgical procedure.', 'The two groups did not differ significantly by age, gender, body weight or length of surgical procedure. Although baseline IFT was significantly lower in Group M than in Group T (33.8 degrees C vs. 35.1 degrees C), it increased during the procedure by 1.2 degrees C in Group M compared to a 0.2 degrees C increase in Group T. Baseline CT was also lower by 0.5 degrees C in Group M compared to Group T (NS), but CT increased in Group M by 1.0 degrees C compared to 0.2 degrees C in Group T, resulting in similar final CTs.'] Is intravenous fluids warming by mattress simple and efficient during pediatric surgery?