If it is true that small children chronically swallow toothpaste while brushing their teeth, the possibility exists that the use of a fluoride toothpaste during infancy might result in the ingestion of sufficient F to cause mottling in their permanent teeth. In order to test this hypothesis, the infant siblings of children participating in the clinical trial of a dentifrice containing 2% sodium monofluorophosphate were examined 6–8 years afterwards, following the eruption of their permanent teeth. No hypoplasia or mottling were found which might be attributed to the ingestion of undesirable amounts of monofluorophosphate toothpast