To investigate pesticide use and prevention practices of tangerine growers in Fang district, Chiang Mai province in Northern Thailand. A questionnaire survey of 312 farmers in the study area, in-depth interviews and group discussions. Only 36% of the participants pursued the recommended prevention practices every time they used pesticides. Methomyl which is on the watch list of chemicals was used by 87.8% participants. Cultivating experience and pesticides use experience contributed significantly to the use and prevention practices of growers, while the attendance in the training program did not contribute in the same way. The farmers rather believed in their experiences and those of their neighbors. Education, training and research into harmful effects and the health and environmental costs of pesticide use are needed. The extension workers can go directly to weak points and narrow their intervention plan to alter the pesticide policy instead of providing basic knowledge on pesticides again and again. Knowledge of pesticide prevention practices did not make tangerine growers protect themselves against pesticides or reduce their exposure to chemicals. The training program did not work as the key of extension and should not be presented as one. (Contains 9 tables and 2 notes.)