The controlled release behaviour of bleomycin hydrochloride microcapsules was investigated by an in vitro dissolution method and an in vivo antitumour test. Bleomycin hydrochloride microcapsules prepared using the highest cooling rate exhibited sustained release characteristics and its release rate obeyed a nearly zero order release kinetics. Microcapsules containing bleomycin hydrochloride were locally injected into the solid tumour of uterine cervix carcinoma bearing nude mice. Tumour growth was markedly inhibited by treatment using bleomycin hydrochloride microcapsules compared to the control group and the group receiving direct local administration of bleomycin hydrochloride. No significant differences in the changes of body weight after treatment were found between the control group and the treated group. These results suggest that controlled release microcapsules may be applicable as a drug carrier for delivery of antitumour agents in cancer chemotherapy.