In liver injuries, the quiescent hepatic stellate cells (HSCs) promptly change to activated HSCs, which are easily identified by the intense immunoreactivity for alpha-smooth muscle actin. However, reproducible markers for quiescent HSCs in formalin-fixed, paraffin-embedded liver tissue sections have not yet been reported. We immunohistochemically examined the expression of vinculin, one major protein of dense plaques, on cultured LI90 cells and on HSCs in normal and diseased human and rat livers. In cultured LI90 cells, vinculin appeared as small linear patches. Although vinculin was consistently negative in the routine liver tissue sections, an antigen retrieval technique using microwave oven heating yielded excellent effects. Using this technique, the formalin-fixed, paraffin-embedded human and rat normal liver tissue sections showed the vinculin immunoreactivity along the sinusoidal wall. Immunoelectron microscopic observation of hepatic parenchyma demonstrated that the vinculin was exclusively expressed in quiescent HSCs. In fetal rat livers, vinculin-positive quiescent HSCs gradually increased in number with gestation. In diseased livers the activated HSCs showed more intense immunoreaction for vinculin. These results indicate that, using microwave pretreatment, vinculin is expressed in quiescent and activated HSCs in routinely processed liver tissue sections. It could allow us to evaluate the development and distribution of quiescent HSCs and to examine the relationship between quiescent and activated HSCs.