The purpose of the study is to determine the toxicity and feasibility of non-myeloablative allogeneic hematopoietic cell transplants for multiple myeloma from unrelated donors.

The primary objective of the protocol is to evaluate the toxicity and tolerability of this mixed chimerism matched unrelated donor allogeneic transplant approach for patients with multiple myeloma. Response, toxicity, survival and graft-versus-host disease will be evaluated.

Inclusion Criteria:a) Multiple myeloma which is responsive to therapy. Eligible patients may have early or relapsed disease. Patients must have Stage II-III disease or have progression after initial treatment of Stage I disease. Patients who have relapsed following autologous transplantation may be eligible for this protocol.

b) Age <= 60 years. c) No prior therapy which would preclude the use of low-dose total body irradiation.

d) Patients must have their pathology reviewed and the diagnosis confirmed at Stanford University Medical Center. Patients with smoldering multiple myeloma, monoclonal gammopathy of unknown significance, or amyloidosis will be excluded from this study.

e) Patients must have a Karnofsky performance status > 70%. f) DLCO >= 60% predicted. g) ALT and AST must be < 2X normal. Total bilirubin less than 2 mg/dl. h) Serum creatinine < 2.0 or 24-hour creatinine clearance >= 50 ml/min. i) Patients must be HIV negative. j) Pregnant or lactating women will not be eligible to participate. k) Patients must provide signed, informed consent. Exclusion Criteria:a) Severe psychological or medical illness b) Patients who have undergone prior allogeneic hematopoietic cell transplantation will not be eligible for this study.

c) Patients who have an HLA-identical sibling donor will be excluded