Levels of anti-streptokinase antibodies were measured in 75 Indian patients who were divided into three groups. The first group consisted of 25 healthy blood donors; the second group of 25 patients with ischaemic heart disease with stable angina; and the third group of 25 patients with acute myocardial infarction. The mean level of anti-streptokinase for the entire group was 0.37 SD 0.20 million international units (IU) (range 0.09 to 1.15 million IU). There was no significant difference in the anti-streptokinase levels among the three groups. In order to neutralise the anti-streptokinase levels in 90% of the study population, 0.57 million IU of streptokinase was necessary. These levels are more than twice the current Western levels. In the light of this study, it may be necessary to reconsider the adequacy of the conventional dosage of streptokinase while treating acute infarctions in India and, possibly, other tropical countries where prevalence of prior streptococcal infection is high.