This open-label study will assess the pharmacokinetics, efficacy and safety of RO5185426 administered as 240mg tablets in previously treated patients with metastatic melanoma. Patients will be randomized to receive one of four dose-levels of RO5185426 [RG7204; PLEXXIKON; PLX4032] orally twice daily on days 1 to 15 (morning dose). Starting on day 22, treatment with RO5185426 may be resumed at a dose of 960 mg twice daily and continued until disease progression. Target sample size is <100 patients.