The article focuses on the functional impact of tumor-associated fibroblasts (TAF) on its surrounding cells. It intends to cover the recent knowledge on TAF, the phenotype, and expression profile of which have been described in the first part of the review series (Kunz-Schughart and Knuechel, 2002). The present review is subdivided into two main chapters: (1) functional impact of TAF on tumor cells and (2) fibroblast-host cell interactions in tumor tissue. In the first paragraph of chapter (1) about the role of fibroblasts in tumor cell growth and differentiation it is revealed, how strongly cellular interaction is dependent on fibroblast and tumor cell type as well as the spatial ratio between the cells. The variation of cellular behavior depending on quantity of molecules holds also true for the group of ECM molecules, e.g. the balance between MMPs and TIMPs, which provide an interesting therapeutic target in tumor tissue. This is one of the topics addressed in the second paragraph which focuses on tumor cell dissemination. Chapter (2) addresses the relation of TAF to other intra- or peritumoral host cells. The hypoxia-related angiogenesis induction of fibroblasts via growth factor secretion (e.g. VEGF) is considered as important as the immune modulatory properties of fibroblasts on immune cells, such as monocytes/macrophages. These cellular properties can be tested under controlled conditions in three-dimensional heterologous cultures of human cells, providing the chance for systematic modification to assess therapeutic effects in an in vivo like environment.