Alloys used as implant materials release metal ions to surrounding tissues. Cytotoxic substances attack at the molecular level, and these effects are reflected in the structure of the cells and organelles. The objective of this study was to evaluate the cellular morphology and ultrastructural changes of cultured human gingival fibroblasts to salt solutions of ions (beryllium (Be+2), chromium (Cr+6 and Cr+3), nickel (Ni+2), molybdenum (Mo+6)) which may be released from nickel-chromium dental alloys. The concentrations chosen were based on previously conducted cell culture studies. Fibroblasts were exposed to the different ion concentrations for 24 or 72 h. Cellular morphology and ultrastructural features were examined using scanning electron microscopy and transmission electron microscopy. Ultrastructural alterations observed included irregular shaped nuclei for cells exposed to hexavalent chromium and nickel, pseudopodia for cells exposed to beryllium and molybdenum, and lipid droplet formation in cells exposed to nickel.