The purpose of the present study was to evaluate the bond strength of four adhesive systems to dentin. Twelve human third molars had their occlusal enamel removed in order to expose a flat dentinal surface, on which the adhesive procedures were carried out. The teeth were divided into four groups, according to the employed adhesive system and composite resin: Group 1 - Single Bond + P60 (SB); Group 2 - Bond 1 + Surefil (B1); Group 3 - Prime Bond NT + Alert (NT); and Group 4 - Prime Bond 2.1 + TPH (2.1). After 24 h in distilled water at 37 degrees C, the teeth were longitudinally sectioned in two perpendicular directions in order to obtain parallelogram-shaped specimens with a cross-sectional area of 0.8 mm2 and 10 mm of length, on the average. The test specimens were submitted to microtensile test. The data were submitted to ANOVA (alpha = 0.05), which revealed no differences between the groups, although the analysis of the specimens that presented early fracture evidenced the lower sensitivity of the SB system.