Summary.The antibacterial activity of four elements (zinc, copper, fluoride and mercury), previously reported to be released from dental restorative materials, was investigated. This was carried out using two aerobic micro‐organisms isolated from dentine beneath cavities in the ferret. These were grown in the presence of the test elements over a concentration range of 10–100 μg/ml for 72 hours. Concentration and exposure time were found to have a highly significant effect on the growth and viability of both micro‐organisms. Zinc, mercury and copper exerted the greatest effect, fluoride the