Determination of biocompatibility and cytotoxicity is part of the initial evaluation of medical devices stipulated by ISO standards on biological evaluation of medical devices. Cell culture systems for testing biological reactions to drugs, biomaterials or treatment techniques used in various disciplines have been gaining importance. A wide variety of cell lines are commonly used: cultured fibroblasts from human skin, buccal mucosa, periodontal membrane or embryonic lung; epithelial and HeLa cells; cultures of human keratinocytes and HaCaT cells; different murine cell lines (C3H-L, Balb/c 3T3, L929 and others) as well as murine cells cultured from liver and spleen; T lymphocytes from lymph nodes and macrophages obtained by lavage. All these cells are suitable for the use in biocompatibility tests. Nevertheless, the general opinion is that cytotoxicity tests in vitro will be more convincing when performed with cells that are homologous with the human tissue concerned. In accordance, appropriate cell lines for the use in cytotoxicity and tolerance tests concerning the skin would be human dermal fibroblasts and human epidermal keratinocytes, as they take an active part in the immune response, inflammatory processes and wound healing.