The antiplaque potential of zinc salts has been previously demonstrated. The purpose of the present investigation was to establish the effect of zinc chloride dentifrices on plaque growth and on the concentration of zinc in saliva and plaque. Ainc levels in saliva and plaque were measured by atomic absorption spectrophotometry. Elevated zinc levels were observed in saliva and in plaque for 1 hour after contact with a zinc chloride dentifrice. Increased concentrations of zinc were also observed in plaque residue. Further analysis of data showed that subjects with high rates of plaque growth benefited more from the zinc dentifrices than did those with low rates of plaque growth.