In a prior study we showed evidence that latex from Carica candamarcensis contains a protein fraction that stimulates mammalian cell proliferation. In this report we describe the isolation of two proteinases responsible for this effect. Both proteinases (P1, P2) display a relative mass of 23 kDa and following chromatographic purification stimulate proliferation of fibroblastic and epithelial cells. P2 added to L929 fibroblasts at 2.5 nM enhances proliferation by 60 %. We further demonstrate that its cellular effect is linked to an increase in activity of Erk2, a component of the MAP kinase pathway. To our knowledge, this is the first known plant proteinase to exert a proliferative effect in mammalian cells. This novel mitogenic property attributed to a purified cysteine proteinase may explain some of the therapeutic actions attributed to these enzymes.