This article discusses the types of reperfusion injury, some of the causes of the injury and the possible role of the radical scavengers in protecting against it. The methodological problems that have plagued this field are explored and some answers put forward, although we are sure that further questions will have been raised. There are now reasons to question the use of the tetrazolium staining procedure which has become the "gold standard" for measurements of infarct size. It seems likely that it is adequate only as a screening procedure, and even then will be associated with a troublesome number of false positives. Collateral flow is an important determinant of infarct size and simultaneous measurements of collateral flow are essential in the interpretation of the effects of drugs on infarct size. The limitations of the various animal models are important when relating experimental findings to the clinical condition. After a decade of research, reperfusion injury is itself still under question, and there remains confusion as to the role that oxygen-derived free radicals may play in the ischemic/reperfused myocardium. However, we believe that, from the experimental data available, oxygen derived free radicals are involved in the overall pathophysiology of ischemia and reperfusion, although the full extent remains to be clarified and the therapeutic implications explored.