A doping‐vehicle dependence of the relative substitution of Nd at the two non‐equivalent Ca sites in fluorapatite has been verified. By implication, similar differences may be expected for other rare‐earth dopants in other apatites. Detailed structure refinements based on especially reliable single‐crystal X‐ray diffraction data from (i) undoped, (ii) Nd2O3‐doped, and (iii) NdF3‐doped synthetic fluorapatite were used. An analysis of ratios of site‐occupancy factors, based on Nd3+‐for‐Ca2+as the substitution model, led to the conclusions that (i) Nd substitutes at both Ca(l) and Ca(2) sites in approximately equal atomic fractions in the NdF3‐doped material and (ii) Nd substitutes only at the Ca(2) site in the Nd2O3‐doped material. These results correlate well with reports that neodymium‐doped fluorapatite crystals prepared as solid‐state laser hosts differ in spectra, growth rate, and laser quality with the sour