PCN was dissolved in olive oil and given to rats intraperitoneally. The effect of PCN on liver mitochondria was compared with control rats given olive oil only. The results were as follows: The RCI of liver mitochondria had decreased significantly one hour after the injection of PCN. It was slightly decreased after 24 hours. The ADP/O ratio was slightly decreased one hour and 24 hours after the injection of PCN. The TBA value of the PCN injected group had increased significantly after 1 and 24 hours compared with the control, indicating that peroxidation of liver lipid had occurred. The level of ATP had decreased significantly compared with that of the control group 24 hours after the administration of PCN. Liver mitochondria showed greater uptake of components with shorter retention times than of those with longer retention times.