<正> Platelet aggregation ratio （PAR） was assessed in 45 patients with severe viralhepatitis （SVH） with Born’s method.The PAR of normal individuals

patients with acuteicteric hepatitis

and those with chronic active hepatitis were also studied to serve ascontrols.It was found that PAR decreased markedly in SVH patients

which was marked in theearly stage of SVH

more marked in the intermediate stage

and most marked in the latestage.The changes of PAR were in negative correlation with those of serum total bilirubin

and in positive correlation with those of prothrombin activity.The reduction of PAR inSVH patients might be ascribed to the defect of platelets themselves as revealed bycross-over experiments.The results of this study indicate that PAR may be useful in judging the severity ofSVH patients since the degree of PAR reduction parallels closely with the severity of liverdamage.Finally

the condition of platelets in vivo and in vitro in SVH patients werediscussed.