Demineralization of enamel by acid buffer and the use of protective agents to combat it were studied by two different techniques, one using intact enamel surfaces and the other powdered enamel. Compared with the acknowledged protective effect of fluoride, calcium glycerophosphate was the most effective phosphate compound. Sodium phytate and calcium sucrose phosphate gave less consistent results. Applied topically, α-glycerophosphate was more effective than β-glycerophosphate. Pretreating the enamel with saliva or a protein solution improved its resistance to the attack of acid buffer but reduced the apparent effectiveness of the protective agent