To investigate the effect of self-etching bonding systems on the control of pulpal haemorrhage in direct pulp exposures by observing the contraction of pulp blood vessels using the rat carotid artery model. Six dentine-bonding agents (Mac Bond, One-Up Bond F, Clearfil SE Bond, FL Bond, Prompt L-Pop and Prime&Bond NT) were used. The efficacy of bonding agents were compared with that of epinephrine for dose and the contraction forces (vasoconstriction) induced on the smooth muscle and the results recorded using a force displacement transducer. Dose-dependent relaxations caused by the test materials were recorded in the same manner in comparison with papaverine. FL Bond, SE Bond, One Up Bond, Mac Bond produced dose-dependent relaxations, while Prompt L-Pop and Prime&Bond NT produced epinephrine-like contractions on the rat carotid artery. For self-etching primers, which produce vascular relaxation, haemorrhage control with additional chemicals should be considered if direct pulp capping is to be performed using such adhesive systems.