Kupffer cells (KCs) are located in the liver sinusoids adjacent to hepatocytes and are capable of producing important growth-regulating mediators which exert both stimulatory and inhibitory influences on hepatocyte proliferation by paracrine mechanisms. To elucidate the overall effect of KC-depletion on liver regeneration, mice were selectively and long-standing depleted of KCs by liposome-encapsulated dichlormethylene diphosphonate. Using in vivo fluorescence microscopy, immunohistochemistry, Western blot analysis, NF-B transcription factor DNA binding activity and cytokine assays, livers of KC-depleted and KC-competent mice were analyzed at day 3, 5 and 8 after partial, i.e. 68% hepatectomy (PH). Selective KC elimination delayed cell proliferation, as given by significantly reduced PCNA and cyclin B1 protein expression in liver tissue at day 3 post PH. This was associated with a lower liver weight at day 8 upon PH. Resection-associated activation of NF-B with translocation into parenchymal and nonparenchymal cell nuclei was diminished in livers of KC-depleted mice, primarily at day 3 after PH. KC-depleted mice further lacked the resection-induced rise in TNF- and IL-6 serum concentrations. These findings imply that KCs play a stimulatory role in liver regeneration, mainly by activating NF-B with influence on the cell cycle, and by enhancing expression of the proliferative cytokines TNF- and IL-6.