1. Marker enzymes for the principal subcellular organelles of rat liver were asayed in the liver of rats 1 day and 8 days after bile-duct ligation or after laparotomy as a control procedure.
2. The microsomal enzymes in liver tissue showed complex changes. Benz[α]pyrene hydroxylase activity, predominantly found in the smooth endoplasmic reticulum, was decreased. Glucose 6-phosphatase activity and ribonucleic acid, which are localized predominantly in the rough endoplasmic reticulum, were increased.
3. The plasma membrane enzyme, alkaline phosphatase, increased in activity after bile-duct ligation.
4. No changes in mitochondrial enzyme activities were noted after 1 day but there was a 50% reduction 8 days after ligation. Lysosomal enzyme activities did not change in the liver tissue.
5. Liver catalase and d-amino acid oxidase activities showed a slight increase at 1 day post-ligation but a significant fall by 8 days.
6. Lactate dehydrogenase, a cytosol enzyme, showed a decrease in activity after 1 day but an increase in tissue activities 8 days after ligation.
7. Serum activities of mitochondrial, plasma membrane, microsomal, lysosomal and cytosol marker enzymes tended to increase post-ligation, particularly at 8 days.
8. Monoamine oxidase, a predominantly mitochondrial enzyme, was greatly elevated in the serum after 1 day but had returned to normal activities by 8 days.