The addition of calcium glycerophosphate (CaGP) to commercial sodium monofluorophosphate (NaMFP) can increase significantly the capacity of NaMFP to protect hydroxyapatite discs and human enamel segments from subsequent acid attack. The improvement in activity which is equivalent to that achieved by a threefold increase in the NaMPF concentration occurs at molar ratios in the region of 10:1 (NaMFP:CaGP) although increasing the proportion of CaGP to give equal molar ratios actually impairs the NaMFP activity. At the optimum ratios, the benefit can be demonstrated in water or simulated saliva solutions. The combination can also be formulated successfully into a conventional toothpaste. The improvement is attributable to an increase in the uptake of fluoride in a form which is not alkali-soluble at the expense of the alkali-soluble fraction which will contain calcium fluoride.