The cytoskeleton has been shown to form a network, connecting the extracelluar matrix via integrin with the nucleus and the cytoplasmic constituents of the cell It is therefore assumed that the cytoskeleton may mediate signals generated by perturbations originating in the matrix. The purpose of this study is to examine the effect of cytoskeletal change on osteoblastic cell activities. The author cultured osteohinstic cells obtained from neonatal mouse calvaria The cells were treated with cytochalasin B(CB) or colchicine (COL) at four concentrations for 3 hours and after another 24 hours the conditioned media was collected and assayed for prostaglandin E₂ (PGE₂), interleukin-6(IL-6), tumor necrosis factors (TNF-a) and matrix metalloproteinase-1(MMP-1). In addition, the cytoskeletal protein actin were observed by immunofluorescence. The results were as follows: 1. The production of PGE₂ showed the tendency to be increased in CB-treated group. PGE₂ was increased in COL-treated group dose-dependantly. 2. IL-6 Production, in CB-treated group, was increased, except at 1.0 µg/ml. IL-6 was induced in COL-treated group. 3. TNF-a production was increased in CB-treated group, except at 1.0 hg/ml, and in COL-treated group, that was increased. 4. The MMP-F production was decreased in CB-treated goup and was not changed in COL-treated group, which could be selectively visnai zed by immunoblotting with monospecific antibody. 5. The cytoskeletal actin stress fibers were disappeared and the cells showed to be rounded in CB-treated group. These results indicated that there are a relationship between the cytoskeletal rearrangements and osteoblastic cell activities, especially in release of paracrine/autocrine factors, such as PGE₂, IL-6, and TNF-a.