Alloreactive NK cells are considered rather save concerning the development of graft-versus-host disease (GVHD) (1–5), although a high number of activating killer-cell immunoglobulin-like receptors (KIR) (6) or extensive NK cell stimulation (7) might promote GVHD, maybe due to remaining T-cells in the graft. The gene discussed is KIR3DL2; the disease is graft versus host disease.