Mullerian Inhibiting Substance (MIS), a gonadal growth factor important in sexual differentiation, has antiproliferative activity against several human carcinoma cell lines. In this study, we examine the effect of MIS-transfection on the growth characteristics of Chinese hamster ovary (CHO) and human ocular melanoma (OM431) cells, compared to wild-type lines and a CHO line transfected with a noncleavable, inactive MIS mutant. MIS-transfection inhibited proliferation of CHO cells in double-layer agarose, tumor spheroid, and murine subrenal capsule assays, as well as growth of CHO and OM431 cells in pulmonary metastasis studies. These results anticipate further study of targeted gene therapy of certain human tumors with MIS gene constructs.