Chitoean is a natural chelating agent. It is derived from chitin which is a cellulose-like biopolymer distributed widely in nature, expecially in shellfish, insects, fungi, and yeast. The purpose of the present study is to investigate whether orally given water soluble chitosan can eliminate intraperitaneally injected radiostrontium (Sr-85) in mice, Water soluble chitoaan and usual food was mixed as 10:90 by weight. The mixed food were fed for 60 (group 1) or 90 days 4poup 2). No chitosan was given to the control group. Each group consiets of 5 miee. Sr-85 (0.2 uCi) was intraperitoneally injected after completion of prefeeding of usual or mixed food. The same food was given for more 5 days. The aniraals were sacrificed at the 6th day. Isolated apmee, s, femurs, tibias, teeth, and tails were eounted by a gamms caunter. The retention of Sr-85 in bones was signifi*cantly lowere in the prefeeding groups (p