The synthesis of fibrinogen in rat hepatocytes can be induced two to three times its normal level following an injection of turpentine. Detection of the increased synthesis of this protein was accomplished by quantitative immunoprecipitation analysis. The time sequence for maximal intracellular synthesis occurs more rapidly than the concomitant rise in plasma fibrinogen, implying that the secretion of fibrinogen is somewhat slower than was anticipated. Binding studies with 125I-labeled anti-fibrinogen to the nascent chains on the ribosomes showed no detectable changes in the radioactivity distribution before or after stimulation as analyzed by zone sedimentation. It was estimated that only 4.4% of the total polysomes were involved in fibrinogen synthesis prior to induction and this was increased to 15% following turpentine stimulation. The results suggests that the rise in fibrinogen synthesis during the acute-phase response was related to an increase in functional messenger RNA transcripts rather than in an increase in the rate of protein synthesis.