Using a rotating wall vessel (RWV) bioreactor, which simulates a microgravity environment for cells, approximately 150 osteosarcoma MG63/collagen sponge composites (3 mmϕ x 3 mm) were three-dimensionally cultured simultaneously in a cylindrical vessel (250 ml) to produce the same number of cancer tissues of an equal size and quality. Then, these tissues were exposed to the anticancer drug doxorubicin, and dose dependence of the effect of this drug on the viability of the cells was examined compared with a conventional two-dimensional culture system. The dose-dependent effect on three-dimensional tissues was markedly different from the two-dimensional culture because of differences in the culture systems.