Remarkable results of the treatment of refractory multiple myeloma with thalidomide have been reported. In most preceding studies, the given thalidomide dose was escalated to a maximum tolerated dose of up to 800 mg/d. The frequency of adverse effects correlates with dose intensity. Since a significant gain of therapeutic effects could not be observed as thalidomide dosage was escalated, the optimal dose of thalidomide remains to be determined. We report the results of a study with low dose thalidomide (median administered dose 100 mg/d, range 50-400 mg/d). Twenty-four relapsed (n = 19) or resistant (n = 5) multiple myeloma patients were included in the study. Twelve patients (50%) received thalidomide as monotherapy, 8 patients (33%) received a combination of thalidomide and dexamethasone (every 4 weeks 40 mg/day for 4 days) and 4 patients (17%) who were resistant to vincristine, doxorubicin, dexamethasone (VAD) received VAD combined with thalidomide. Overall, a response was observed in 12 patients (50%). Of the 12 patients treated with low dose thalidomide alone 5 (42%) responded, of the 8 patients who received a combination of thalidomide and dexamethasone 5 (63%) responded and of the 4 patients who had thalidomide in addition to VAD 2 patients (50%) responded. In 3 patients, thalidomide treatment had to be discontinued because of side effects and 1 patient died before response could be assessed. We conclude that low dose thalidomide is an effective and safe rescue therapy in relapsing or refractory multiple myeloma. Response to thalidomide might be dependent on prognostic parameters and tumor burden. To answer these questions larger prospective studies are necessary.