OBJECTIVE--To investigate the release of chemoattractants after myocardial ischaemia during balloon angioplasty. DESIGN--Sampling of femoral arterial and coronary sinus blood before and immediately after the first balloon inflation during angioplasty. In a study group of 16 patients the balloon was kept expanded for two minutes, whereas in a control group of eight patients the first balloon inflation was brief (< 10 s). MAIN OUTCOME MEASURES--Chemotaxis of neutrophils from healthy donors towards patient plasma (Boyden chamber), superoxide anion production by normal neutrophils after incubation with patient plasma (cytochrome C reduction). RESULTS--In the study group, coronary sinus plasma after balloon deflation was more chemoattractive to normal neutrophils (median relative increase 24% (quartiles: 4%, 45%), p = 0.008) and induced a higher superoxide anion production in normal neutrophils (44% (10%, 97%), p = 0.013) than arterial plasma. Concomitantly, the degree of activation of patient neutrophils was increased in coronary sinus blood compared with arterial blood, as shown by an increased proportion of neutrophils reducing nitro-blue tetrazolium (21% (9%, 38%), p = 0.006) and a decreased neutrophil filter-ability (-16%(-3%, -40%), p = 0.003) in coronary sinus blood. In the study group before balloon inflation and in the control group before and after balloon inflation differences between arterial and coronary sinus blood were not significant. Signs of ischaemia (lactate release, ST segment changes) were only detected in the study group. CONCLUSION--After transient myocardial ischaemia during balloon angioplasty there is a local release of chemoattractants, associated with neutrophil activation.