Symptom-limited Naughton and modified Bruce treadmill exercise protocols were compared in 20 patients to assess their ability in detecting additional ischaemic abnormalities six weeks after myocardial infarction. Eleven patients had a result indicating reversible myocardial ischaemia on both tests while the other nine had no ischaemic abnormality during either of the two protocols. The only significant difference between the two protocols was the longer exercise duration resulting from the Naughton protocol (17.3 +/- 5.0 vs. 14.8 +/- 2.8 mins, P less than 0.01). The mean maximum heart rates, rate-pressure products and achieved workloads did not differ significantly. We conclude that even though the Naughton protocol resulted in a significantly longer mean maximum exercise duration, the protocols were equally effective in detecting additional ischaemic abnormalities six weeks after myocardial infarction.