Earlier studies from this laboratory have shown that the complement system, especially the component C3, in female B6C3F1 mice is suppressed following TCDD exposure in vivo. However, the direct exposure of TCDD in vitro does not affect the C3‐producing capacity of two types of hepatoma cells, as well as mouse primary hepatocytes. To investigate the effect of TCDD on C3 production by the liver following in vivo exposure, liver intracellular C3 levels and pro‐C3, the precursor of the secreted C3, were examined in the present study. The results demonstrated that there was a dose‐dependent increase of liver intracellular C3 levels (from 138% to 175% of control) immediately following TCDD (from 10 to 40 μg/kg) exposure. This increase was rapid (4 h after exposure), but transient (less than 2 h), and was not accompanied by an alteration of serum C3 levels. Studies using sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PACE) analysis showed that the increase in liver intracellular C3 levels resulted from, at least partially, an increase in intracellular pro‐C3. Serum C3 levels did not decrease until d 3 after exposure, when both liver intracellular C3 levels and pro‐C3 in TCDD‐treated mice were not different from those of the control mice. These results indicated that the modulation of liver intracellular C3 by TCDD did not correlate with the suppression of serum C3 levels following exposure.