Between January 1993 and February 1994, 106 patients whose internal mammary arteries were to be used for revascularization to treat coronary artery disease were examined for a prospective study of papaverine administration. The mean blood flow in the internal mammary artery was 59.9 mL/min +/- 7.3 mL/min before papaverine administration. The patients were divided into 3 groups: in Group I papaverine was administered intraluminally, retrograde in the internal mammary artery; in Group II, it was administered topically; and in Group III, it was administered perivascularly, in the pedicle. After papaverine administration, the mean blood flow in Group I was 135.7 mL/min +/- 10.1 mL/min; in Group II, it was 84.8 mL/min +/- 8.3 mL/min; and in Group III, it was 136.3 mL/min +/- 9.7 mL/min. The highest increases in blood flow were observed in Group I (105.3%) and in Group III (112.6%). On the basis of our results, we recommend that papaverine be injected perivascularly into the pedicle of the internal mammary artery, since retrograde injection can cause dissection.