Cylinders of Fuji Type II glass ionomer restorative cement were bonded to the superficial dentin layer of young bovine incisor teeth that had previously been subjected to 4 different treatments: 1) teeth immersed in 35% hydrogen peroxide for 60 min and etched with 37% phosphoric acid gel for 60 s; 2) teeth immersed in saline for 60 min and etched with 37% phosphoric acid for 60 s; 3) teeth etched with 37% phosphoric acid for 60 s and immersed in 35% hydrogen peroxide for 60 min; or 4) teeth etched with 37% phosphoric acid for 60 s and immersed in saline for 60 min. Specimens were stored in water at 37° for 1 and 7 days, prior to tension and shear testing. A total of 128 teeth were tested: 8 teeth in each group for each day and for each test. Statistical analysis of the results indicated that there was a highly significant reduction in bond strength of the cement when dentin was exposed to hydrogen peroxide as compared with saline. SEM examination of randomly selected fractured test specimens indicated that bond failure was cohesive in nature, suggesting that the hydrogen peroxide treatment adversely affected the setting process of the glass ionomer cement.