Data on toothbrushing habits were collected during a 3-year caries clinical trial of sodium monofluorophosphate toothpastes in Lanarkshire, Scotland, involving 3,005 schoolchildren of mean age 12.5 years at baseline. Stated normal brushing frequency and oral rinsing method after brushing were recorded. Half the panel indicated they rinsed their mouths after toothbrushing using a beaker. The proportion of the panel brushing once per day or more increased during the trial. Differences in oral habits were observed between the sexes, with 42% of girls and 52% of boys being non-beaker rinsers and 73% of girls, but only 44% of boys, brushing their teeth at least twice per day. Twice-a-day brushers had a consistently lower caries increment than less frequent brushers. This was also seen in the baseline prevalence data, but did not account for all incremental differences noted. Subjects using beakers had consistently higher increments than non-beaker rinsers. Again, this difference could not be explained by variations in baseline prevalence. Differences in the caries increment were also observed between boys and girls, these appearing to be linked both to the cumulative effect of male/female habit variations plus a difference in the baseline caries prevalence. A dose response to the three fluoride levels, i.e 1,000, 1,500, and 2,500 ppm F, was seen for the different habit combinations which again could not be explained by differences in the baseline caries prevalence.