This trial is investigating the use of blood stem cells autologous peripheral blood derived stem cells in conjunction with chemotherapy in the treatment of prostate cancer. The trial is being conducted by the Department of Medical Oncology at St Bartholomew's Hospital London and proposes to recruit 39 subjects. Stem cells will be collected from the blood following administration of Granulocyte Colony Stimulating Factor (G-CSF) which releases the blood stem cells from the bone marrow. Patients with castration resistant prostate cancer will be given their own stem cells as well as Melphalan. Participants will be monitored for complications and assessed fro changes in their clinical condition.