In order to study the regimen of the McMurdo Ice Shelf three holes, 31, 32, and 57 m deep, were drilled near the seaward edge of the shelf; ice thicknesses at the drill sites were calculated to be 33, 48, and 94 m respectively. The rate of melting at the bottom of the shelf was found to be 1 m per year at two drill sites. The vertical density gradient in each of the holes is larger than that observed at Little America Station, and the density increases abruptly by about 0.1 g cm−3at the top of a brine-soaked layer which was estimated to be less than 6 m thick in each hole. Temperature profiles can be explained on the assumption that the brine moves horizontally through the shelf from the seaward edge to the interior and supplies heat to the shelf by convection and by liberation of latent heat during freezing. The observed brine level in the holes is about 20 percent lower than the hydrostatic level.