In testing for the cytotoxicity of medical devices, crucial parameters are the type of cells, the duration of the exposure, the physical form of the device and the method of evaluation. Using cell cultures the changes of cell functions induced by artificial materials may be evaluated. In screening tests the effect of biomaterials on functions common to all cell types is investigated through both continuous lines and primary cultures. In supplementary tests the effect of biomaterials on specific functions is studied, employing cells of the same type of those which will be in contact with the device in vivo. Osteoblasts, either from primary culture or an established line, are used to study the interaction with materials for bone implants. We evaluated whether dental cements affect the replication cycle of osteoblast-like cells MG63. The S phase was inhibited by the cements with a phenolic group, even though to a different extent. Mononuclear cell cultures are used to investigate the immune response, which is important in the host reaction to implant. We investigated whether the chromium ions released in a biological fluid may induce PBMC to produce cytokines involved in bone resorption. Chromium extract did not impair TNFalpha release significantly, but inhibited IL-6 release significantly in stimulated PBMC. Endothelial cell cultures are useful to the evaluation of materials for vascular grafts. We studied the influence of some types of Dacron on endothelial functions. Collagen-coated Dacron decreased significantly the production of 6-keto-prostaglandin F(1alpha). Knitted Dacron caused a significant increase of tissue factor, a significant reduction in PECAM-1 and a significant increase in ELAM-1.