To determine the effects of different surface moisture on the bond strength of an ethanol/water-based (Single Bond [SB]), an acetone-based (One-Step [OS]), and a water-based (Syntac Single Component [SC]) adhesive system to dentin. On 90 human third molars, a flat superficial dentin surface was exposed by abrasion with 600-grit SiC paper. The adhesives were applied to a delimited area of 52 mm2 according to the manufacturers' instructions on either dry (oil-free air/30 s) or rewetted surfaces (1.5, 2.5, 3.5, 4.0 or 4.5 µl of distilled water), and composite crowns were constructed incrementally. After storage in distilled water at 37°C for 24 h, the teeth were longitudinally sectioned in the "x" and "y" directions to obtain bonded sticks with a cross-sectional area of 0.8 mm2. The specimens were tested in tension at 0.5 mm/min and the fracture mode analyzed. Resultant bond strength was expressed as an index that includes bond strength values of the different fracture patterns and the specimens that failed during preparation for the microtensile testing. The data was analyzed by two-way ANOVA, Tukey's multiple comparison, and regression analysis. Highly significant main effects and interaction (p 0.0001) were detected. A quadratic relationship between the bond strength index and the surface moisture was identified (R2 = 0.95, p 0.001). SB showed a maximum bond strength (42.2 ± 6.7 MPa) that was statistically similar (p = 0.4996) to the maximum bond strength of OS (40.1 ± 4.6 MPa), although obtained at a different degree of moisture (ca 1.5 µl for SB and 3.5 µl for OS). SC showed its maximum bond strength (27.7 ± 3.9 MPa) with 1.5 µl moisture. SB presented its highest bond strength at 1.5 µl of water, which was significantly higher than the bond strength obtained at any other degree of moisture (p 0.05). OS achieved its maximum bond strength at 3.5 µl of water; however, that value was not statistically different (p > 0.05) from the values obtained with 1.5 µl to 4.0 µl of water. Similarly, highest bond strengths obtained with SC were not different (p > 0.05) within the range of 0 µl to 3.5 µl of water. All adhesive systems tested had a different moisture spectrum in which higher bond strengths were obtained. SB and SC performed better on a drier substrate, while OS showed better performance on wetter substrates. OS and SC had a broader range of moisture within which maximal bond strength could be achieved.