This article reports results of a study of 563 practicing Minnesota and Wisconsin dental hygienists' knowledge and opinions about fluorides and water fluoridation. Two independent samples were selected randomly from the populations of licensed dental hygienists residing in the two states. Data were collected using a pretested, 42-item, mailed questionnaire. An 84 percent response was achieved with two followup reminders. These data provide baseline information about the caries prevention knowledge and attitudes of practicing dental hygienists in two states. Respondents from both states held similar levels of knowledge about fluorides and opinions about decision making on fluoridation. Fluoride topics, especially water fluoridation, were not receiving high priority in patient education, although nearly all believed that dental hygienists should promote water fluoridation actively. Two-thirds of respondents from both states believed fluoridation decisions should be made by health authorities, rather than by elected officials or through public vote. Greater attention to patient education about fluoride and community water fluoridation is needed by dental hygienists.