We investigated the clinical applicability of the lymphocyte proliferation test (LPT) in chromium contact sensitivity. 6 out of 8 chromium-sensitive patients were positive in the LPT, whereas none of 8 non-chromium-sensitive controls responded in vitro to tri- or hexavalent chromium compounds. LPT thus appeared to offer an additional diagnostic tool in chromium sensitivity. We also studied cellular interactions in 4 of our chromium-sensitive patients. Sensitized T-lymphocytes could be activated to proliferate only in the presence of accessory cells, of which epidermal Langerhans cells (LC) appeared more efficient than blood adherent cells.