Poly(L-lactide-co-glycolide) (PLG) was modified through the adsorption of collagen to improve the behaviour of fibroblasts and osteoblasts. As reference materials cell-resistant polystyrene (PS) and cell-conductive tissue-culture polystyrene (TCPS) were also evaluated. The physicochemical surface properties of the materials were studied by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and water contact angle measurements. The morphology of cells was examined using optical microscopy, while their growth was evaluated by both crystal violet and MTT tests. Nitric oxide level and protein concentration were tested in cell supernatants. The results showed that the adsorbed amount and the organization of the adsorbed collagen were influenced by surface hydrophobicity. Cell culture experiments on native substrates revealed that cell attachment, spreading and growth enhanced, depending on the substrate, in the following order: PS<PLG<TCPS. Coating the substrates with collagen led to distinct changes in the cell behaviour: the cells were more numerous, better spread and more homogeneously distributed on the surface compared to the bare polymers. Improvements in cell growth and protein secretion were also observed. The results obtained show that surface modification of PLG by simple adsorption of collagen promotes the distribution and proliferation of fibroblasts and osteoblasts.