PKC412, a selective inhibitor of protein kinase C (PKC), is currently in clinical trials as an anti-tumor drug. In the present study, we investigated the anti-metastatic effect of PKC412 using an experimental metastatic mouse model intravenously injected with melanoma cells. One-hour exposure to various concentrations of PKC412 (0.5, 5 and 50 microM) dose-dependently reduced the lung-metastatic potential of highly metastatic B16-F10 and -BL6 mouse melanoma cells in syngeneic mice. Following the exposure, PKC activities in B16-F10 and -BL6 cells were significantly decreased, but growth curves were not influenced. To elucidate the mechanism of the anti-metastatic effect of PKC412, we examined the activity to invade the extracellular matrix and the platelet-aggregating activity of the melanoma cells incubated with PKC412 (0.5, 5 and 50 microM) for 1 hour. PKC412 significantly reduced both the invasive and platelet-aggregating activities. These results suggest that PKC412 shows an anti-metastatic function through the inhibition of the invasive and/or platelet-aggregating activities of melanoma cells. PKC412 is potentially a promising candidate for an anti-metastatic agent.