Purpose: To evaluate the bond strengths of an etch-and-rinse adhesive and a self-etching adhesive to human dentin in vitro and under two in situ conditions: non-anesthetization and anesthetization of the teeth with a local anesthetic containing vasoconstrictor. Materials and Methods: An in situ study was performed on 49 maxillary premolars scheduled for extraction due to orthodontic reasons. For the bond strength test, occlusal cavities were prepared either with or without a local anesthetic containing vasoconstrictor. The cavities were bonded with Adper Single Bond or Clearfil SE Bond and filled with a resin composite, Filtek Z250. The teeth were then extracted, sectioned, trimmed, and tested for microtensile bond strength. For the observation of dentin surfaces, 20 premolars were used. The impressions of the cavity floors in the anesthetized and non-anesthetized groups were taken before and after acid etching. The replicas were observed under a scanning electron microscope. In vitro, the bond strength test and the SEM observation were also carried out on 24 extracted premolars with the same procedures used in the in situ study. Results: The bond strengths of the two adhesives bonded to dentin in situ were significantly lower than those in vitro. When both adhesives were tested under in situ conditions, there were no significant differences between the bond strengths to dentin of anesthetized and non-anesthetized groups (p > 0.05). No fluid droplets were found on dentin on the cavity floor prepared in vitro, either before or after acid-etching. For the unetched dentin prepared in situ, fluid droplets were found and covered on the smear layer in anesthetized and non-anesthetized groups, but the droplets were slightly larger in the non-anesthetized group. In the non-anesthetized, acid-etched group, dentin surfaces were covered with coalescent dentinal fluid in most specimens. However, in the anesthetized, acid-etched group, patent tubules and some dentinal fluid were observed on the surfaces. Conclusion: It was concluded that in situ, dentinal fluid had a detrimental effect on the dentin bond strengths of an etch-and-rinse adhesive and a self-etching adhesive. However, reduction in dentinal fluid due to the effect of a local anesthetic containing vasoconstrictor did not improve the bond strengths in either adhesives. Keywords: local anesthetic, microtensile bond strength, dentin adhesive, in situ experiment