In this study, interface pressures, transcutaneous oxygen tension (TcPO2), and blood flow were compared with the classic pressure ulcer-prone areas in the supine and lateral position on six different high- and low-air-loss support surfaces. Interface pressures were substantially higher in the lateral decubitus than in the supine position. Consistent with this, mean TcPO2 and blood flow readings over the trochanter in the lateral position were lower than over the sacrum and ischium in the supine position. With weighting, the average TcPO2 readings decreased from 78.6 mmHg to 11.9 mmHg on the trochanter and from 65.4 mmHg to 45.7 mmHg on the sacrum and ischium. In parallel, average laser Doppler readings decreased from 2.3 to 0.7 laser Doppler flow units over the trochanter, but did not change significantly over the sacrum and ischium. These data support the clinical suggestion that the lateral decubitus position should not be maintained for long periods of time, not even on many special support surfaces.