The effects of topically applied mouthrinses containing AlCl3, or AlK(SO4)2 on dental caries and plaque were investigated in a rat model. For comparison, NaF and a two-step treatment of AlCl3 and NaF were also tested. Six groups of 20 weanling rats were inoculated with Streptococcus sobrinus 6715 and provided a caries-inducing diet and distilled water ad libitum. Test agents were topically applied twice daily 5 days per week at a concentration of 0.037 mol/l in a mouthrinse vehicle and were compared with a vehicle control rinse and a distilled water control. After 10 weeks none of the treatments reduced plaque amounts relative to the controls. The AlCl3 and AlK(SO4)2 rinses significantly reduced both smooth-surface and sulcal caries by approximately 40%. The cariostatic activity of the aluminum rinses was equivalent to an equimolar NaF mouthrinse on smooth surface lesions, but was statistically less than NaF on sulcal caries. The two-step treatment with AlCl3 and NaF indicated numerically additive effects, but the results were not statistically better than with NaF alone. Dentine caries progression paralleled the enamel caries prevalence results. No deaths, toxicologic effects, or inhibition of growth rates were observed in any treatment group. This study confirmed that topically applied solutions of aluminum salts inhibited caries formation in the rat caries model and showed that the cariostatic activity of aluminum was maintained in a compatible mouthrinse vehicle.