Allergic or anaphylactic-like reactions have been reported with cis-dichlorodiammineplatinum(II) (CDDP) administration. We have seen two reactions among 50 patients treated in a phase II trial of CDDP. Both patients were successfully rechallenged after diphenhydramine pretreatment, and therapy was continued. In vivo and in vitro studies performed in one patient included negative skin tests, negative histamine release assay, negative lymphocyte stimulation studies, and normal total serum IgE. We conclude that some apparent allergic reactions occurring with CDDP may have a non-allergic etiology, and treatment may be successfully continued in selected patients.