Hip implants containing cobalt–chromium (CoCr) have been used for over 80 years. In patients with metal-on-metal (MoM) hip implants, it has been suggested that wear debris particles may contribute to metal sensitization in some individuals, leading to adverse reactions. This article presents data from a study in which the popliteal lymph node assay (PLNA) was used to assess immune responses in mice treated with chromium-oxide (Cr₂O₃) particles, metal salts (CoCl₂, CrCl₃, and NiCl₂) or Cr₂O₃ particles with metal salts (“A preliminary evaluation of immune stimulation following exposure to metal particles and ions using the mouse popliteal lymph node assay” (B.E. Tvermoes, K.M. Unice, B. Winans, M. Kovochich, E.S. Fung, W.V. Christian, E. Donovan, B.L. Finley, B.L. Kimber, I. Kimber, D.J. Paustenbach, 2016) [1]). Data are presented on (1) the chemical characterization of TiO₂ particles (used as a particle control), (2) clinical observations in mice treated with Cr₂O₃ particles, metal salts or Cr₂O₃ particles with metal salts, (3) PLN weight and weight index (WI) in mice treated with Cr₂O₃ particles, metal salts or Cr₂O₃ particles with metal salts, (4) histological changes in PLNs of mice treated with Cr₂O₃ particles, metal salts or Cr₂O₃ particles with metal salts, (5) percentages of immune cells in the PLNs of mice treated with Cr₂O₃ particles, metal salts or Cr₂O₃ particles with metal salts, and (6) percentages of proliferating cells in the PLNs of mice treated with Cr₂O₃ particles, metal salts or Cr₂O₃ particles with metal salts.