Purpose: To evaluate high-dose melphalan followed by autologous stem- cell transplantation in patients with refractory multiple myeloma. Patients and Methods: Multiple myeloma patients with alkylating agent or vincristine/doxorubicin/dexamethasone-refractory disease were eligible for the phase II multi-institutional Southwest Oncology Group trial S8993. Patients up to age 70 years were enrolled between April 15, 1991, and May 1, 1996. Patients without prior stem-cell collection were primed with high-dose cyclophosphamide (HD-CTX; 6 g/m2) and granulocyte-macrophage colony- stimulating factor. After stem-cell procurement, patients received melphalan 200 mg/m2 with autologous transplantation. Upon recovery from melphalan, patients were to receive interferon alfa-2b until relapse. Results: Seventy- two patients were enrolled onto S8993; five were ineligible and one received no therapy. Of the 66 assessable patients, 56 patients underwent the transplant procedure; 54 were assessable for response and 56 for toxicity. The response to HD-CTX (n = 37) included three complete remissions (CRs; 8%) and five partial remissions (PR; 14%); response to melphalan (n = 54) included 16 CRs (30%) and 19 PRs (35%), for an overall CR and ≥ PR (n = 66; intent-to-treat) of 27% and 58%, respectively. Toxicities included six treatment-related deaths: two during HD-CTX and four during transplantation. The median progression-free survival (PFS) and overall survival (OS) durations on an intent-to-treat basis from transplant registration was 11 months and 19 months (95% confidence interval, 14 to 29 months), respectively. The 3-year actuarial PFS and OS rates were 25% and 31%, respectively. Conclusion: High-dose therapy with melphalan 200 mg/m2 is feasible with high response rates (58% overall) and an OS of 19 months in patients with refractory multiple myeloma.