We measured the compressibility of La(2)Mg(16)Ni, LaMg(2)Ni, LaMg(3), and gamma-La to 30.1 GPa by synchrotron X-ray diffraction. The bulk moduli are respectively determined to be 54, 67, 57, and 47.5 GPa. The strengthening of the compounds by the addition of nickel is insignificant. The compressibility is dominantly determined by that of La and Mg. The strength increases of the compounds relative to pure La and Mg elements is comparable to that caused by solid solution strengthening. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.