The use of chemotherapy in treating retinoblastoma is presently increasing in importance. Because of the rarity of this disease, excellent in vitro chemosensitivity assays are necessary, not only for individualized testing but also for the development of chemotherapy regimens. It is instructive for improving such assays to discuss in vitro chemosensitivitly tests of tumor cells from clinical specimens according to a cell biological perspective. This review will first summarize and discuss the technical problems encountered with several representative in vitro chemosensitivity tests on clinical specimens, including retinoblastoma. The second part of this review will summarize the results of chemosensitivity tests on retinoblastoma specifically.