According to ‘antagonistic compensation’, appendicular bones rendered hypofunctional by surgical means, become shorter and more robust. In normal Buffalo rats, appendicular bones are short and very robust and in Fisher rats they are long and gracile. Total body constitution is robust in Buffalo rats and gracile in Fisher rats. In GRL rats, appendicular bones are short but body constitution is gracile and the robusticity of the appendicular bones is intermediate between Fisher and Buffalo rats. Thus, total body constitution and relative length of the appendicular bones determine their robusticity, shorter bones being more robust than longer bones. In other words, the relationship between bone length and robusticity is the same in experimentally produced antagonistic compensation and genetically determined normal condition of r