Hysteretic heating of the crack tip often occurs during tests of fatigue crack propagation. If hysteretic heating occurs to a significant extent at and ahead of the crack tip in a notched polymer specimen, fatigue crack propagation behavior may be altered in a complex way. It is, therefore, important to monitor the temperature at crack tips during testing. Methods of temperature measurement are reviewed, and a semiautomated apparatus incorporating an infrared microscope for measuring temperature profiles during fatigue tests is described.