The effect of multi-porous beads prepared from 80% deacetylated chitin on the activation of mouse peritoneal macrophages was examined. Deacetylated chitin bead (DAC-bead) preparations were shown to activate macrophages for tumoricidal activity depending on the increasing concentration of acetic acid used for the pretreatment of beads. The large DAC-bead was more susceptible to treatment with acetic acid than small DAC-bead, and showed more potent capacity for the activation of macrophages under the same pretreatment conditions with acetic acid. Deacetylated bead preparations, on the other hand, showed less activities. In addition, DAC-bead pretreated with acetic acid stimulated macrophages to produce interleukin 1. The possibilities of multi-porous beads as cancer chemotherapeutic-carrier were examined by the method of column chromatography and of in vitro antitumor experiment. Forty-four percent of adriamycin adsorbed on the surface of and in bead was released within the first 60 min. of elution, and then adriamycin was released more slowly in proportion to the elution time. Antitumor activity of adriamycin-adsorbed bead was less effective than that of free adriamycin if they were compared on the basis of total content of adriamycin.