A 3-year, double-blind caries trial was conducted to evaluate the caries-reducing effect of a modified technique to use toothpaste. At the outset, 369 children, 4 years of age, were randomly assigned to four groups. At the end of the study, when the children were 7 years old, 281 (76%) had completed the trial. Two of the groups (test groups, n = 131) were given the following instructions regarding 'toothpaste technique': (1) to spread the paste evenly on the teeth prior to brushing, (2) not to expectorate more than necessary during brushing, (3) to filter the remaining dentifrice foam in the dentition, together with a sip of water, by active cheek movements for 1 min before expectorating, and (4) not to carry out any further water rinsings afterwards, and not to eat or drink for 2 h after brushing. The children in the other two groups (control groups, n = 150) were not given any instruction how to use the dentifrice and how to rinse after the brushing, but were, as the children in the test groups, encouraged to use the test dentifrice and to brush their teeth twice daily. Two commercial fluoride dentifrices (A and B) were compared: one of the test groups and one of the control groups used each product. Approximal carious lesions were scored on bite-wing radiographs at baseline and at the end of the study on the distal surface of the first and on the mesial surface of the second primary molars. No difference in caries increment was found between toothpastes A and B. The children in the two test groups developed a mean of 1.14 new dfs during the 3 years compared to 1.55 in the two control groups (p < 0.05). Thus, the results indicate that the modified toothpaste technique reduced approximal caries in preschool children by an average of 26%.