We assessed the hydration state of antlers and its effect on antler mechanical properties compared with wet femur. Red deer antlers were removed from the head at various times, from a few days after velvet shedding till late in the season, and weighed weekly until after casting time. Antlers cut just after losing their velvet lost weight rapidly in the first few weeks, then settled down and changed weight very little, the latter changes correlating with air relative humidity. Antlers cut later showed little weight change at any time. The water content of cortical and trabecular parts of the contralateral antler was assessed after cutting. Most of the weight loss was from the cancellous, not the cortical, part of the antler. Wet and dry specimens from the antlers, and wet specimens from deer femora, were tested mechanically. Compared with wet bone, wet antler had a much lower modulus of elasticity and bending strength, but a higher work to fracture. Compared with wet bone, dry antler showed a somewhat lower Young's modulus, but a considerably higher bending strength and a much higher work to fracture. The impact energy absorption of dry antler was much greater than that of wet bone. In red deer, the antler is effectively dry during its use in fights, at least in southern Spain. In addition, dry antler, compared with ordinary bone, shows mechanical properties that suit it admirably for its fighting function.