The cytotoxicities of oxides, phosphates and sulphides, which possibly form on dental alloys, were tested using the 'agar method'. The relative magnitudes of the cytotoxicities of these compounds exhibited tendencies similar to those of the metal components in the compounds. In correlation with dental amalgams, zinc oxide was the most cytotoxic, just as with metallic zinc, while tin oxides and mercury oxides exhibited no cytotoxicity. Zinc was the most influential element in the cytotoxicity of dental amalgams. On the other hand, in correlation with Ni-Cr alloys, Co-Cr alloys, and/or stainless steels a chromium oxide and a cobalt oxide showed serious cytotoxicity, whereas the iron oxides were non-cytotoxic. Sulphides, which possibly form on silver alloys, showed cytotoxicity. Oxides and phosphates of titanium and aluminium, and hydroxyapatite, were not cytotoxic, supporting the use of these materials for implants. Not only the valence of an element but also the chemical species combining with the element affect the cytotoxicity of the alloy containing it.