The expression of ferritin genes has been studied in two well differentiated hepatoma cell lines, HepG2 and Hep3B, and in an undifferentiated cell line, HepPLC/PRF/5. The steady-state level of the H and L ferritin subunit mRNAs is different in the three cell lines, being most abundant in the HepG2 and Hep3B cells. The efficiency of promotion of transcription of the H and L gene promoters is not correlated with the levels of the two transcripts; moreover the half-life of the H and L mRNAs varies among the hepatoma cells. The different level of ferritin mRNAs in differentiated and undifferentiated cells appears to be mainly due to a different stability of the transcripts.