The present invention is a method for using an improved guiding catheter that eliminates the need for an introducer sheath or a separate Tuohy-Borst "Y" adaptor, thus reducing the time and expense for performing artery opening procedures. Furthermore, the guiding catheter with straightening dilator as described herein allows the hole in the wall of the femoral artery in the groin, or even more advantageously, the radial artery in the arm to be approximately 2 French sizes smaller in diameter as compared to the hole that would be created if an introducer sheath is also used. The advantages of the present invention are accomplished by utilizing a guiding catheter with a dilator that has a stiffened and/or curved distal section that can be used to straighten the distal section of the guiding catheter as it is advanced through the arterial system. The guiding catheter plus dilator can then be used in a manner similar to an introducer sheath to percutaneously enter the artery by being advanced over a previously placed guide wire. Once the distal ends of the dilator and the guiding catheter are placed near the ostium of the coronary artery, the dilator and guide wire are withdrawn which allows the guiding catheter to assume its normal bent shape (e.g., a Judkin's bend) near its distal end. The cardiologist can then, by well known techniques, place the guiding catheter's distal end in the ostium of a coronary artery. Any of several well known procedures can then be performed including angiography, balloon angioplasty, atherectomy or stent placement.