A REPORT from this Station (Kosin et al., 1952) demonstrated the beneficial effect of the so-called “pre-heating” treatment of the Broad Breasted Bronze males on their subsequent fertilizing capacity. More recently evidence has been presented (Mitchell and Kosin, 1954) to indicate the generally depressing effect of moderately and uniformly warm ambient temperature on the egg laying rate in the Broad Breasted Bronze turkey. It was found that not only the rate of egg production was lowered, but that the average egg size was reduced as well.There still remained unanswered, however, at least two questions: (a) the effect of preheating both sexes and then subjecting them to one of several environmental conditions and (b) the effect of “cooling” the males in the latter part of the mating season on their fertilizing capacity. Accordingly, a study was set up in 1951–52 to obtain answers to these two questions. The present …