ABSTRACT. One of the limiting factors in dairy production in hot climates is heat stress (Costa et al., 2002). Under heat, animals produce less and have lower reproduction rates (Kadzere et al., 2002). Management devices that reduce the impact of high temperature and humidity on the animal are available, but they are not fully efficient and not all production systems can afford them. Higher heat tolerance can be achieved by selecting or crossbreeding more heat-tolerant animals. Crossbreds in dairy cattle have been successful under extensive, but not intensive, management because of much lower production levels than purebreds (McDowell et al., 1996). Therefore, the remaining option is to select more heat resistant purebreds, predominantly Holsteins.