In a retrospective study of 40 patients, we evaluated the effectiveness of the new 5 Fr 0.058" lumen diameter guiding catheter in routine PTCA. A total of 54 balloon angioplasties were performed. The mean age was 62.1+/-12.8 years, with 71% men. The artery dilated was the LAD in 50%, the RCA in 37%, and the circumflex in 13%. Sixty percent of the lesions dilated were proximal lesions, with only 25% defined as distal lesions. Significant calcifications were present in 20% of the lesions. Stents were implanted in 96%, and mean stent length was 14.0 mm, ranging from 8 to 24 mm. Mean balloon diameter was 2.7 mm, ranging from 2.0 to 3.5 mm. The procedure was a success in 95%, with only two failures. No other complications occurred. We concluded that the 0.058" 5 Fr guiding catheter could be suitable in the majority of noncomplex, selected PTCA cases. However, limitations and advantages over the standard 6 Fr technique are yet to be defined.