Northern analysis using total RNAs from the component cells of normal rat liver indicated that COL1A(I) mRNA is present in fat-storing cells (Ito cells) and sinusoidal endothelial cells. A fraction for Kupffer cells also contained this mRNA. When CCl4 was given, COL1A(I) mRNA was increased in a factor of 1.5 in the fractions of these component cells. After 48 h of the drug administration, hepatocytes appeared to possess over 60% of liver COL1A(I) mRNA, although in normal hepatocytes its level was below the range detectable by our procedures. Under this injured condition of liver, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA level was elevated, while activity of this enzyme was lowered by 50% of the control value. All the changes were obviously suppressed by the simultaneous administration of prostacyclin.