Polymerase chain reaction amplification of reverse transcribed RNA (RNA-PCR) was used to isolate overlapping cDNA clones encoding an inducible form of nitric oxide synthase (NOS) from purified rat hepatocytes. NOS gene expression in hepatocytes is dependent upon bacterial lipopolysaccharide (LPS) and cytokine treatment. The predicted amino acid sequence of rat hepatocyte inducible NOS is 94% identical with that from the mouse macrophage cell line, RAW264.7. Differences between the two sequences occur as sporadic amino acid substitutions with no major gaps or insertions. These differences are most likely the result of species variability which suggests that hepatocytes and macrophages express the same NOS gene upon induction.