The aim of this study is to evaluate liver elasticity noninvasively. We have already proposed an ultrasonic imaging system that can reconstruct vibration maps inside tissue under forced mechanical vibration. With this system, shear elastic properties of soft tissue can be evaluated as vibration velocities. Theoretically, these velocities increase with the increase of tissue elasticity. Sonoelasticity imaging was performed on 236 patients with chronic hepatitis and liver cirrhosis, and 50 healthy volunteers. The average of the velocities was 598.8 +/- 151.7 cm/s in healthy volunteers, 984.4 +/- 362.5 cm/s in chronic hepatitis and 1189.0 +/- 411.7 cm/s in liver cirrhosis. The average velocity of Child C group was statistically faster than those of Child A and B groups. Fibrotic rate from biopsy specimens statistically had the strongest positive correlation with velocities. With our system, the degree of liver fibrosis and function can be estimated objectively and noninvasively.