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The concentration of a group of messenger RNAs, some of which are expressed only (or mainly) in the liver and others of which are expressed in all tissues, was examined during liver regeneration. Most of the tissue-specific mRNAs did not change greatly in concentration or in transcription rate, but mRNAs such as actin and tubulin increased by as much as tenfold without an equivalent transcriptional increase. However, the mRNAs for “acute phase” proteins such as serum amyloid A and metallothionine did increase dramatically and increased transcription was easily detected. In addition to these findings, there was no increase in the rate of synthesis of the RNA constituents necessary to make ribosomes, pre-rRNA and mRNA for ribosomal proteins. Thus, the differentiated hepatocyte continues to function as a differentiated cell during the two or so replications necessary for regeneration, and many of the constituents necessary to increase cell mass may be supplied by increased preservation and utilization of transcribed RNAs.