We describe measurements of the stiffness and Young's modulus, Y of single crystals of molybdenum-based compounds. Atomic force microscopy is used first to image, and then to perform stiffness measurements on crystals which are growing up out of a substrate. Y is extracted by comparing the measured stiffness with that calculated from a continuum elasticity model of the crystals, whose experimentally indeterminate parameters are the Young's modulus and the geometry. We find a value for Y in the range 0.8-1.4 TPa, depending on the assumed geometry of the nanocrystal. As these crystals are essentially perfectly ordered on the micron scale, this opens the possibility of forming composite materials of immense strength. (C) 2002 American Institute of Physics.