The macrophage migration inhibitory factor (MIF)-homologue D- dopachrome tautomerase (D-DT) recently has been described to have similar functions as MIF. However, the role of D-DT, as opposed to MIF, in tumor biology remains unknown. We hypothesized that D-DT could represent a target for therapeutic interventions in cancer. We analyzed the production of D-DT in the murine melanoma model B16F10 and the murine breast cancer model 4T1 by western blot and ELISA. D-DT was released by tumor cells both in vitro and in vivo. RT-PCR revealed the expression of the D-DT receptor CD74 on both tumor cell lines. Tumor bearing mice had higher serum levels of D-DT compared to healthy controls. Remarkably, knock-down of D-DT by siRNA reduced proliferation of B16F10 cells in BrDU-assay and rendered them more prone to apoptosis induction, as shown by flow cytometry. In vivo neutralization of D-DT by antibodies reduced tumor progression in the B16F10 subcutaneous syngeneic tumor model. In summary, we could show that D-DT and its receptor are expressed in the murine tumors B16F10 and 4T1. Knock-down of D-DT through siRNA or blocking by antibodies reduced proliferation of B16F10 tumor cells. This qualifies D-DT for further evaluation as a therapeutic target.