Changes in the hardness of Nb--Mo alloys were determined at temperatures up to 2000 deg C under a vacuum of 10/sup -4/ mm of Hg. It was found that in the 20 to 200 deg C range the hardness of all the alloys, except that of pure Nb and Nb + 10 at.% Mo decreases sharply; this is caused by the effect of admixtures, including the dissolved gases. At temperatures up to 900 deg C the alloy containing 50 at.% Mo has the highest hardness, while at still higher temperatui es the maximum is shifted to the alloy containing 60 at, % Mo. In the 200to 700 deg C range the hardness of alloys with 60 to 80 at, % Mo decreases unexpectedly, and the temperature coefficient of hardness has a negative value. An alloy with a composition close to that of NbMo/sub 3/ has the lowest temperature coefficient of hardness. Hardness at high temperatures is a function of the time of loading. (TTT)