Male albino rats, hypophysectomized at 35 days of age, built significantly better nests under conditions of lowered room temperature than did normal controls. "It is assumed that superior nesting is indirectly instigated by deficiency in heat production resulting chiefly from loss of the thyro- and adrenotrophic hormones." The hypophysectomized rats, tested for position preferences in a runway whose ends varied markedly in temperature, preferred the warm end significantly more than did the controls. This was regarded as being in harmony with the nesting results, and was interpreted as "compensatory behavior in hypophysectomized rats whose mechanism for heat production has been impaired." (PsycINFO Database Record (c) 2006 APA, all rights reserved)