The ability of two types of operating table pads to reduce pressure under bony prominences was evaluated. Pressures were measured beneath the occiput, scapula, olecranon, sacrum, ischial tuberosity, and calcaneus of ten normal volunteers in the supine position, and beneath the trochanter major with patients in the lateral decubitus position, on a standard (latex foam rubber) pad and a water-filled, polyurethane foam pad. Both pads failed to reduce pressure below mean capillary pressure, and neither pad was as effective in reducing pressure as cushions currently available for wheelchairs or beds. The water-filled, polyurethane foam pad did reduce pressure beneath the occiput, calcaneus, and trochanter major significantly (P<.01) more than the standard pad. The need for an operating table pad that reduces pressure under bony prominences is discussed, and a practical, theoretically effective cushion is suggested.