The NHLBI PTCA Registry collected clinical data on 3,101 PTCA procedures performed at 105 clinical centers between September 1977 and September 1981. To investigate the "learning curve" from introduction through the early application of this new therapy for revascularization, success rates and complication rates were examined by calendar year and according to investigator experience. Success rates improved by calendar year, from 54% in 1979 to 66% in 1981. Investigators with fewer than 50 cases had a success rate of 55%. After an investigator had performed 150 procedures, the success rate was 77%. The increase in success rate was largely the result of a dramatic increase in the ability to cross the narrowing with the catheter, and was accounted for by experience and improved equipment. Patient selection for PTCA was characterized by sex, age, previous CABG, number of diseased coronary arteries and stable Canadian Heart classification over time. Reflecting the increase in the success rate was the decrease in the need to perform elective CABG. Emergency CABG, death and MI rates were low (1% mortality, 5% nonfatal MI) and did not change significantly with time or with investigator experience.