Besides Macrophages and T-Killer-cells, Natural killer cells (NK) are the third fraction of immune cells capable to attack cancer cells. In many cases, this cell fraction is rather small and out of function. By isolating them from the blood stream and incubating them with several agents, we are capable to pick the ones that are capable of activating this special cell fraction. Results show simple agents like salicylic acid as well as extracts from fungus. Whatever is needed and capable to activate these cells – it should be applied.