Abstract Cu 2+ is cariostatic in rats reportedly due to it bacteriocidal properties. Here, we report the use of a simple abiotic model system to investigate whether Cu 2+ has any inhibitory effect on the acid dissolution of human enamel. Crowns were exposed to a sequence of seven 10 mmol/l acetic acid challenges. The mineral dissolved during each challenge was then determined. CuSO 4 (10 mmol/l) was present during the fourth of these challenges. Loss of calcium and phosphate were reduced by 57 and 63%, respectively, ( P<0.0001) in the presence of Cu 2+. Losses were also significantly reduced during the next acidic challenge in the absence of Cu 2+. The degree of protection was found to approach maximum at about 5 mmol/l Cu 2+. The well-known cariostatic properties of Cu 2+ may therefore be due not only to its ability to inhibit bacterial growth but also to its ability to directly inhibit acid dissolution of enamel.