Effect of sulforaphane on cell-mediated immune response (CMI) was studied in B16F-10 melanomainduced metastasis-bearing C57BL/6 mice. Administration of sulforaphane significantly enhanced natural killer (NK) cell activity in metastatic tumor-bearing animals (43.17% cell lysis, on day 5) and the activity was observed earlier than in tumor-bearing control animals (maximum of 9.76% cell lysis, on day 9). Antibodydependent cellular cytotoxicity also was enhanced significantly in metastatic tumor-bearing animals (41.20% cell lysis on day 9) after sulforaphane administration compared with untreated control tumor-bearing animals (maximum of 12.62% cell lysis on day 15). An early antibody-dependent complement-mediated cytotoxicity also was observed in sulforaphane-treated tumor-bearing animals (26% cell lysis, on day 15). Administration of sulforaphane significantly enhanced the production of IL-2 and IFN-γ in metastatic tumor-bearing animals. In addition, sulforaphane significantly downregulated the serum levels of proinflammatory cytokines such as IL-1β, IL-6, TNF-α, and GM-CSF during metastasis.