This study examined the effect of adhesive systems (either placed as directed or when mixed with composites prior to photocuring) on bond strength and monomer conversion. Occlusal surfaces of extracted human molars were ground flat and Scotchbond Multipurpose(R), Single Bond(R), or Clearfil SE Bond(R) adhesive systems were applied according to manufacturer's directions, mixed in situ with flowable or hybrid composites prior to photocuring. Specimens were prepared for microtensile bond-strength testing, and maximal bond strength at failure was recorded. Adhesives and composites were also placed on a diamond attenuated-total-reflectance unit, and infrared spectra were obtained kinetically. Addition of flowable Scotchbond prior to light-curing increased bond strength; however, no effect on Single Bond and Clearfil SE Bond was observed. The mixture of adhesives with composites resulted in lower monomer conversion for Scotchbond and Clearfil SE Bond.8341699105116