The aim of this study was to determine the shaping ability of ProFile 0.04 taper rotary nickel-titanium instruments with ISO sized tips in simulated canals. A total of 40 simulated root canal made up of four different shapes in terms of angle and position of curvature were prepared by ProFile instruments using the 'crown down' approach recommended by the manufacturer. Part 1 of this two-part report describes the efficacy of the instruments in terms of preparation time, instrument failure, canal blockages, loss of canal length and three-dimensional canal form. The time necessary for canal preparation was on average 5.2 min and was not influenced significantly by canal shape. Three instrument fractures occurred and a further 3 instruments deformed; size 35 instruments failed the most (4) followed by size 30 (2), four of the failures occurred in canals with 40 degrees curves. None of the canals became blocked with debris and change in working distance was minimal. Intra-canal impressions of canal form demonstrated that most canals had apical stops and smooth canal walls whereas all canals had good flow and taper. Under the conditions of this study, ProFile 0.04 taper rotary nickel-titanium instruments with ISO sized tips prepared simulated canals rapidly and created good three-dimensional form.