The potential of a new titanium fluoride (TiF) derivative for caries prevention was tested in a pH-cycling model. Daily treatments with various concentrations (100, 250, and 500 p.p.m.) of TiF were compared with similar sodium fluoride (NaF) treatments given at the same pH. Bovine enamel lesions were subjected to 3 wk of pH cycling. The effects were assessed by analyzing calcium uptake and loss in the re- and demineralizing solutions, respectively, and by post pH cycling microradiographic analysis of the lesions. Treatments with NaF reduced calcium loss, enhanced calcium uptake, and induced overall lesion remineralization. Treatments with TiF derivative gradually caused almost complete inhibition of calcium loss and uptake (lesion 'arrestment'), irrespective of the concentration of the TiF derivative. To test the permanence of protection, sound enamel was pretreated with either TiF derivative or NaF, and demineralized for 14 d at pH 4.4 and 4.6. Calcium loss data show that up to 80% inhibition of demineralization could be achieved for the TiF derivative, which was not possible for NaF treatments. This inhibition was obtained through a combination of concentration and number of treatments. The TiF derivative is a promising agent for the prevention of dental caries, especially when aimed at preventing the onset of caries.