Cultured parenchymal liver cells (PC) were recently recognized to contain (latent) transforming growth factor β (TGF-β) while the expression of TGF-β mRNA remains controversial. This study was designed to analyze PC in different microenvironments (liver in situ, highly purified, isolated, and cultured PC) regarding the qualitative and quantitative content of mature and latent TGF-β protein (immunostainings, enzyme-linked immunosorbent assay [ELISA], and enzyme-labeled fluorescence [ELF] technique). The results were compared with its gene expression (reverse-transcription polymerase chain reaction [RT-PCR]). In all microenvironments, PC contained latent TGF-β, which was partially activated after cell isolation and culture. The amount of total TGF-β (mature plus latent) of latency-associated peptide (LAP) and of latent TGF-β binding protein (LTBP) were shown to decrease during culture. In contrast, TGF-β2 and TGF-β3 mRNA and LTBP-1 and -3 mRNA expression were first detectable after culture. Permeabilization of cell membranes in whole liver and of isolated PC with streptolysin O or carbon tetrachloride, respectively, released TGF-β, a part of which was integrated in the large latent complex as estimated by analytical gel filtration chromatography. The TGF-β released by damaged PC induces paracrine effects on hepatic stellate cell cultures. It stimulates hyaluronan synthesis and antagonizes the effect of mitogenic factor(s) of PC on [3H]thymidine incorporation. The results strongly suggest that the main part of hepatocellular TGF-β is not generated by de novo synthesis but from uptake into the liver in vivo. The immunodetection of preexisting mature TGF-β after isolation of the cells is probably caused by intracellular activation of latent TGF-β The injury-dependent discharge of TGF-β from PC might be an important mechanism for initiation and perpetuation of various forms of chronic human liver diseases.