We have studied changes in peripheral tissue thickness with a novel hand-held ultrasound device during the perioperative course of 60 healthy surgical patients in three different intraoperative body positions. The nil-by-mouth period led to a significant decrease in forehead tissue thickness. Standardized infusion therapy with Ringer's solution at a rate of 8 ml kg-1 h-1 resulted in a gradual increase in tissue thickness, which was significantly different from preoperative baseline values after 90 min. Packed cell volume decreased significantly after the start of infusion and remained low over the rest of the observation time. Different body positions did not influence changes in tissue thickness. We conclude that changes in perioperative tissue thickness in healthy patients can be detected easily by ultrasound, independent of body position. This method may prove useful for the non-invasive assessment of fluid balance state.