Ten patients were studied for each of the sizes 2, 3 and 4 laryngeal mask airways (LMA) in order to calculate the pressure exerted by the cuff upon the pharyngeal mucosa. Using a non-invasive method of comparing intracuff pressures recorded both in vitro and in vivo, the transmitted pharyngeal mucosal pressures were calculated over the clinical range of injection volumes. Cuff inflation with the "normal" injection volumes recommended resulted in the residual volumes of the cuffs being exceeded. The intracuff pressures recorded with the mask in situ at these normal injection volumes were in the range 103-251 mm Hg. The calculated transmitted mucosal pressures were substantial for all three sizes of cuff and potentially exceeded the capillary perfusion pressure of the adjacent pharyngeal mucosa, despite apparent pharyngeal accommodation to the mask.