Abstract-Time course change in platelet function on liver damaged mice was studied by a whole blood aggregometer.The liver damaged animals were pro duced by single and multiple injections (p.o.) of 20% CCI4 in olive oil to ddY mice (6 weeks).Platelet aggregation and ATP-release were induced with collagen (final conc. of 2 ag/ml), ADP (final conc. of 20 ,aM) and arachidonic acid (AA: final conc. of 100 ttM). After a single injection of CCI4, platelet counts increased at 5 and 12 hr, and then they decreased from 24 to 120 hr. Multiple injections of CCI4 resulted in a significant increase in platelet counts.A single injection of CCI4 suppressed aggregation by collagen at 24 and 48 hr and diminished the rate of ATP-release from 12 to 48 hr. AA-induced platelet aggregation was depressed at 48 hr, and ATP-release was also diminished from 24 to 72 hr after a single injection. ADP-induced platelet aggregation was decreased 24 and 48 hr after a single in jection and at 48 hr after multiple injections, while, the rate of ATP-release by ADP was significantly increased after single and multiple injections.These changes in platelet functions might be consistent with our original report on the alterations in coagulative and fibrinolytic activities with CCI4-induced liver injury.