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The synthesis of tumor necrosis factor-α has been suggested to be regulated at both the transcriptional and translational levels in response to stimulation by bacterial lipopolysaccharide, although the relative contribution of these two mechanisms has not been quantitatively evaluated. Here, using the murine monocytic cell line RAW 264.7 as a model system, we show that steady-state TNF-α mRNA levels increase ∼77-fold following treatment with lipopolysaccharide for 2 h and to a maximum of 164-fold after 8 h as measured by an RNase protection assay. The TNF-α gene transcription rate increases ∼5-fold following exposure to lipopolysaccharide for 2 h as measured by a nuclear run-on assay. TNF-α mRNA stability did not change in the presence of lipopolysaccharide. A ribosomal sedimentation assay and an RNA transfection assay revealed that the translation rate of endogenous as well as transiently …