In the Begg Technique, factors controlling the anterior intrusive force provided by the archwire have yet to be fully clarified. The rationale for bite opening with very light forces, the effect of Class II elastics on intrusive Force magnitude and the intrinsic qualioy of "Australian" wire in bite opening are examined in this paper. A formulais is presented which allows the intrusive force that archwir exert in different individuals to be predicted. The values derived from the formula were compared with cose model measurements. it was found that the intrusive force of the archwire was afreeted by the length of th e indi vidual dental arch. The magnitude of this in trusive force was seen to increase gradually during the period of bite opening and appeared to be related to the use of Class II elastics. The study revealed factors which aiffected the magnitude of the intrusive force.