Bone tissue loss due to injury or disease often requires application ofautologous tissue grafts or artificial biomaterials to fill the fracture. Synthetic biomaterials provide temporary structural support for bone tissue and can be subsequently colonized by host tissue-specific cells. One of the most investigated groups of biomaterials are degradable polymers that naturally decompose in tissues with time. In particular aliphatic polyesters such as polylactides were reported to fulfill biocompatibility requirements as they induce a minor or lack an immune response and integrate with the surrounding tissue. Here we report on the biological effects of two polymers: poly(L-lactide) (PLLA) and a copolymer of L-lactide and trimethylene carbonate (PLTMC) on osteoblasts (MG-63) and fibroblasts (L-929). Osteoblasts are bone forming cells that are in the closest contact with the potential implant while fibroblasts produce the stroma forming the extracellular matrix (ECM) and along with macrophages initiate inflammation. We detected that both types of cells adhered better to PLLA than to PLTMC which might be related to the more rough surface of the former. However, both polymers, but especially PLTMC, increased apoptotic death of both cell types. Moreover, in contrast to PLLA, PLTMC modulated the production of some immune-related mediators by fibroblasts: it increased nitric oxide production and synthesis of numerous pro-inflammatory factors, cytokines (TNF-a and IL-6) activating leukocytes, and ECM-degrading MMP-9 which facilitates leukocyte migration. Thus, overall, our data suggest that PLTMC is less cytocompatible than PLLA.