The aim of this study was to examine in vitro cell compatibility of the orthodontic base resins Orthocryl (Dentaurum) and Wil-o-dont (Wilde) using the method described by Heidemann and Lampert (1980). The acute local nonspecific cytotoxicity of these materials and that of their individual components were evaluated. Used were both a qualitative microscopic assessment of cytopathological changes occurring in human gingival fibroblasts cultured along side the specimens and a semiquantitative assessment of the zones of inhibited cell growth around the specimens. Whereas Orthocryl and its components exhibited no toxic influence on the growth of the cultured cells, substantial cytotoxicity was observed in the tests of Wil-o-dont. The monomer and the adhesive component of this resin were found to be particularly toxic under the conditions tested. On the basis of the results of the study Wil-o-dont can not be given a clean bill of health in relation to the cytotoxicity of the product.