Data are presented indicating marked antineoplastic activity for cis-dichlorodiammineplatinum(ll) in MOPC 104E myeloma. One-eighteenth of the dose that produced 100% cures can be combined with noncurative, low doses of cyclophosphamide and 1,3-bis(2-chloroethyl)-1-nitrosourea to produce antineoplastic activity of the same degree as that produced by much higher dose regimens which regularly produce cures. Since, in the past, results of therapeutic trials in plasma cell tumors in humans have paralleled results in this animal model, clinical trials of cis-dichloro-diammineplatinum in multiple myeloma appear warranted. © 1977, American Association for Cancer Research. All rights reserved.