The purpose of this study was to assess dentists' knowledge about fluorides as well as their prescription practices. The study population consists of all general and pediatric dentists in Houston, and the sample consists of 360 general and forty-one pediatric dentists. Data were collected with a self-administered mail questionnaire, which consisted of thirteen open-ended and twenty-nine precoded items. After three mailings, the effective response rate was 46.4 percent. Respondents had been in practice on an average of 18.9 +/-6.6 years; the majority were male. More than 75 percent of respondents believed fluoride level in drinking water is an important determinant of fluoride supplement prescription, and 29 percent felt the same about a patient's weight. The correct ages at which to begin (six months) and to discontinue (sixteen years) the fluoride supplements to children were identified by 14.7 and 14.9 percent of the respondents, respectively. Only 6.7 percent of those prescribing fluoride supplements routinely tested the fluoride level in the patient's drinking water. Even though pediatric and general dentists differed in certain items, the two groups did not differ significantly in prescribing fluorides (OR=2.4, 95% CI=0.94, 6.27). Deficiencies and ambiguity in respondents' fluorides knowledge as well as prescription practices indicated a need for educational interventions.