The use of the serum troponin T (TnT) level as a means of assessing minor myocardial injury, which affects the long-term prognosis, has not been fully clarified in patients with coronary artery disease in whom a coronary stent has been implanted. We measured the TnT level to determine the incidence of myocardial damage associated with stent implantation. A total of 29 patients who underwent successful stent implantation (stenting group) were studied and compared with 45 patients who underwent successful coronary balloon angioplasty during the same period (balloon angioplasty group). The serum TnT level was measured by enzyme immunoassay 36 hours after the stenting or balloon angioplasty. The activities of serum creatine kinase (CK) and its isoenzyme MB (CK-MB) were measured by a modified Rosalski method and an immunoinhibition method, respectively, before, immediately after, and 6, 12, and 24 hours after the procedure. Elevation of the TnT level was found in 3.4% (1/29; 0.35 ng/ml) of the patients in the stenting group and in 8.9% (4/45; 0.75 +/- 0.21 ng/ml) of those in the balloon angioplasty group. Elevation of the CK and CK-MB activities was found in 3.4% (1/29; 163 IU/l) and 0%, respectively in the stenting group, and 15.5% (7/45; 375 +/- 143 IU/l) and 4.4% (2/45; 24 and 49 IU/l), respectively, in the balloon angioplasty group. TnT elevation was not invariably accompanied by CK or CK-MB elevation, or by angiographically visible side branch occlusion. For TnT, CK-MB activity and CK activity, there was no significant difference between in the incidence of elevation in the balloon angioplasty group and that in the stenting group. In summary, the incidence of myocardial damage associated with stent implantation seems to be low and comparable to that associated with balloon angioplasty. Despite the low incidence, measurement of the serum TnT level in addition to CK-MB measurement is essential in assessing minor myocardial damage.