Implant tablets (30 mg) containing 2.5, 5 and 10 mg of irinotecan hydrochloride (CPT-11) were prepared using poly (d, l -lactic acid-co-glycolic acid) copolymer as a matrix. Drug release was checked using a buffered solution (pH 7.4), and the antitumor effects were examined using either ascitic P 388 leukemia-or solid Sarcoma 180-bearing mice. Each tablet exhibited gradual release with an 80% release after incubation for 30 d. The tablets containing 5 mg and 10 mg of CPT-11 showed similar release profiles, while the release from the tablet containing 2.5 mg of CPT 11 was lower over 3 weeks after the start of incubation. All tablets showed a high antitumor effect against ascitic P 388 leukemia following the intraperitoneal administration, when the acute toxicity was reduced. On the other hand, following intratumoral administration in mice with Sarcoma 180 solid tumor, the antitumor effects of the tablets were weak and tended to be lower than that observed after treatment with the CPT-11 solution.