Invasive thymoma recently has been shown to be sensitive to combination chemotherapy and in some cases to be relatively indolent. Two cases of extensive thymoma which responded to primary treatment with a combination of a platinum compound (carboplatin or cisplatin), doxorubicin (Adriamycin), and cyclophosphamide (or PAC) are described. Tumor progression occurred 14 (case 1) and 60 months (case 2) after completion of initial PAC therapy and was treated with the same regimen resulting in a second remission, which lasted 6 months in case 1 and is continuing at 8 months in case 2. Similar reports of secondary responses using the same chemotherapy have been described in breast, lung, and ovarian cancers, as well as in Hodgkin's lymphomas. Our observations suggest that retreatment with the same platinum-based regimen should be considered in patients who have progressive thymomas following a previous chemotherapeutic response and a disease-free interval of greater than 12 months.