Mixed valence compounds of general formula R(2-x)Ca(x)BaNiO(5) were synthesized and X-ray diffraction data revealed that they crystallize with orthorhombic symmetry, space group Immm, with the Ca2+ and R(3+) ions randomly distributed in the 4j crystallographic positions of the lattice. Systematic variation of the lattice parameters with an increase in x is observed. The magnetic properties of these doped oxides are quite different from those reported for pure R(2)BaNiO(5) oxides. Doping produces a breakdown in the one-dimensional antiferromagnetic correlations of the nickel sublattice, and the data obtained appear to indicate the appearance of three-dimensional antiferromagnetic ordering for these doped samples at low temperatures.