Irrigation of the root canal is carried out to remove the smear layer and the overlying pulp tissue remnants and dentin chips left by preparation. Our results show that even high volume irrigation is less effective in the apical section than towards cervical. A positive effect of activated continuous irrigation was demonstrated above all in the apical third of the root canal. Almost complete removal of both the smear layer and the overlying debris was achieved. Since high volume, continuous activated irrigation is superior to any other form of irrigation, particularly in the apical section, the results of our studies suggest that further efforts to develop such a root canal irrigation system to the state in which it can be clinically used are necessary.