We report ab initio calculations of the structures, magnetic moments, and electronic properties of Ni(7)-xRu(x) clusters (x = 0-7) using a density-functional method that employs linear combinations of pseudoatomic orbitals as basis sets, nonlocal norm-conserving pseudopotentials, and the generalized gradient approximation to exchange and correlation. The pure clusters Ni(7) and Ru(7) were predicted to have octahedral and cubic structures, respectively, and the binary clusters were found to be either decahedral (Ni(6)Ru, Ni(5)Ru(2), and Ni(4)Ru(3)) or cubic (Ni(3)Ru(4), Ni(2)Ru(5), and NiRu(6)). For Ni(5)Ru(2) and Ni(4)Ru(3) we found a magnetic cooperative phenomenon, which is due to both geometrical effects and electronic contributions through Ni-Ru hybridization.