BACKGROUND: Smaller guiding catheter had a problem with poor backup support during the transradial coronary intervention which resulted in higher failure rate. This study sought to prove the usefulness of deep seating technique which improves the backup support of the guiding catheter required to deliver interventional materials during the transradial coronary intervention. METHODS: Thirthy-five patients(23 males) were included in this study since March 1998 to August 1999. Clinical presentation of these patients were stable angina(7 patients), unstable angina(17 patients), acute myocardial infarction(11 cases). The mean age was 68+/-8 years. The treated vessel was left anterior descending artery in 22, left circumflex artery in 2 and right coronary artery in 11 of 35 vessels. RESULT: Twenty-six lesions were treated with stents, 3 with PTCA, and 6 with rotablator. Procedural success were achieved in 33 out of 35 cases(94%). Guiding catheters were used mostly with 6 Fr(30/35). In the left coronary system, usual Judkins left type was used in most of the patients(24/26, 92%), and in right coronary Judkins, Amplatz and multipurpose catheters were used similiarly. Hypotension and sinus bradycardia was encountered in one case without clinical significance and there was no dissection in all patients. CONCLUSION: Deep seating technique is a safe and effective technique without major adverse event during the transradial coronary intervention in selected cases.