Data from another laboratory have indicated that the individual components of an orthodontic bonding resin might contain a carcinogen. Since that report, the formulation of the product was changed. The purpose of this study was to determine whether the new product is safe. Three groups of rats were used for the experiment. One group served as a control, while the other groups ingested the sealant resin or sealant catalyst. The materials were suspended in an alcohol-aqueous mixture and the solutions were given to the animals as their only source of fluid. The exposure was for 1 year. After this period of time, all the rats were given tap water and observed until day 600. The animals were autopsied at time of death or at the end of the experiment. During the treatment, there were significant differences (p less than 0.01) in water intake among the three groups. The average intake per day for the animals in the control group, the resin group, and the catalyst group was 50.2 cc, 37.8 cc, and 42.2 cc, respectively. Several animals died during the experiment, but there was no significant differences in the life expectancy of the animals in the three groups. The autopsies uncovered one malignant neoplasm, an undifferentiated sarcoma, in a rat from the control group and four benign tumors in rats from the three groups. All of these results indicate that the new formulation of the orthodontic bonding resin is not carcinogenic when ingested at a dose level of 50 ppm.