The mitochondria of the liver celis of rats are counted following the experimerimental operalion of selective and complete bile duct obstruction. The amount of mitochondria decreases significantly aAcr complele obstruction, (in the control group it is 22.948), and after the seleclive obstruction it decreases significantly, too. This experiment suggests: in the compensatory hypertrophy of the liver the amount of mitochondria dosen't inhance.