The effect of time and temperature on the shear patterns of small cylinders from individual choice-grade beef semitendinosus muscles, heated for several hours at 1°C intervals between 50 and 90°C is described.Beef semitendinosus muscle undergoes a marked decrease in shear, approximately one-half eompleted in 11 min at 58°C. This change in shear is a time-temperature rate process having a very high temperature dependence.Minimum shear values were obtained in the range of 60-64'C after heating for 3040 min. In this time-temperature range the collagen shrinkage reaction is completed quickly while the hardening associated with higher heating temperatures is avoided. Relatively large differences, attributed to undefined biological differences, were noted in the shear versus heating time patterns for semitendinosus muscle cylinders from different animals.