The present study investigates the threonine requirements of British United Turkey (BUT) Big 6 turkey toms from 0 to 4, 8 to 12, and 16 to 20 wk of age. Growth, feed conversion, and carcass quality responses to increasing dietary threonine levels were measured. From 0 to 4 wk of age (57 g to 1.1 kg live weight), a dietary threonine level of about 0.95% (3.3 g/Mcal ME) was found to be adequate to obtain optimum growth and feed conversion. From 8 to 12 wk of age (4.0 to 8.6 kg live weight), there was no significant response to dietary threonine beyond the basal level of 0.69% (2.2 g/ Mcal ME). From 16 to 20 wk of age (13.1 to 18.7 kg live weight), a threonine level of about 0.58% (1.8 g/Mcal ME) appeared to be adequate to obtain optimum growth. For optimum breast meat deposition, a higher level in the range of 0.64% (2.0 g/Mcal ME) dietary threonine was required. The present findings may point to the importance of threonine as potentially third limiting amino acid after methionine and lysine in cereal-based turkey diets.