This pilot study reports the effect of fluoride pre-treatment of dentin and enamel on microleakage of a resin bonding agent. Pairs of circular class V cavities involving 50% enamel and 50% cementum were cut in 12 extracted third molars. Each tooth contained a control and a treatment cavity (matched-pair design). A stannous fluoride solution (0.717% SnF2, Gel-Kam, Scherer Laboratories, Dallas, TX) was applied to the entire treatment preparation of each tooth. A dentin resin bonding system (Scotchbond 2 with Scotchprep, a dentin primer, 3M Dental Products Div., St. Paul, MN) was applied per manufacturer's instructions. Silux resin (3M) was placed over the resin bonding agent, light-cured, and finished. The teeth were subjected to 500 temperature cycles between 5 and 55 degrees C. A silver nitrate staining technique was used for evaluation of microleakage. The mean leakage for the control was 2235 +/- 1146 microns, and 2105 +/- 1052 microns for the fluoride treatment sites. It is concluded, from this pilot study with small sample size, that pre-treatment with fluoride of dentin and enamel prior to the placement of a resin bonding agent produced no significant change in microleakage (Student's t test for paired samples, p = 0.6492).