Genistein -a natural flavone compound with antitumor activity- has been proposed as an effective agent to prevent the expression of metastasic capacity in hormone-dependent cancers. The present study represents an effort to assess the efficacy of Genistein in inhibiting the proliferation and expression of the in vitro invasive capacity of tumoral prostatic cells with different invasive potential. In a cell culture system, genistein appeared to be cytotoxic and inhibitory of miaration through a Material barrier to PC-3 cells, the more aggressive invasive cell-line studied. DU-145 and LNCaP cells, which are less invasive than PC-3, are less affected by Genistein both with respect to proliferation rate and inhibition of u-PA and 72 kDa Gelatinase secretion. Measurement of the level of tyrosine-phosphoproteins in the three cell lines studied also showed that PC-3 cells are the most sensitive cells, with a possible molecular target in a membrane-bound protein of 130 kDa.