HSP70 belongs to the heat-shock protein family and binds to unfolded proteins, driven by ATP hydrolysis, in order to prevent aggregation. Previous X-ray crystallographic analyses of HSP70 have shown that HSP70 binds to ADP with internal water molecules. In order to elucidate the role of the water molecules, including their H/D atoms, a neutron diffraction study of the human HSP70 ATPase domain was initiated. Deuterated large crystals of the HSP–ADP complex (1.2–1.8 mm³) were successfully grown by large-scale crystallization, and a neutron diffraction experiment at BIODIFF resulted in diffraction to a maximum resolution of 2.2 Å. After data reduction, the overall completeness, R _meas and average I/σ(I) were 90.4%, 11.7% and 8.1, respectively, indicating that the data set was sufficient to visualize H and D atoms.