Hydroxylapatite (HA) was made containing magnesium, zinc, cadmium, and yttrium. Salts of these cations were added to precipitating HA; the precipitates were dried and sintered at 1100 degreesC for 1 h. Lattice parameters from X-ray diffraction spectra showed that these elements were incorporated into the apatite structure at a level of 2% added fraction of calcium in HA and up to 7% for yttrium. The densities of different substituted apatites were close to theoretical for pressed and sintered samples, which is evidence for low bulk porosity. The grain sizes of substituted apatites were smaller than those of pure HA except for cadinium-containing apatite. Surfaces of etched samples showed no second phases, whereas surfaces of unetched samples showed second phases and higher porosity than etched surfaces. (C) 2001 John Wiley & Sons, Inc.