To investigate the efficacy of dendritic cells and natural killer cells in the inhibition of lung metastasis, we injected dendritic cells and natural killer cells intravascularly into mice bearing B16F10 tumour melanoma cells. This efficiently inhibited tumor growth and prolonged survival. In addition, surviving mice developed a long-lasting memory response against the original tumor when re-challenged with live tumor cells. Intravenous administration of dendritic cells and natural killer cells may be a potential way to treat lung metastasis in patients.