Secretory responses of plasma insulin, glucagon, cortical and glucose to heat exposure (33°C, 60% RH) were investigated using Holstein calves. Plasma gluagon concentration had a significant increase, but plasma insulin, cortisol and glucose had significant decreases within 24 h following heat exposure. Concerning subsequent responses to heat exposure, plasma glucagon level maintained increased concentrations for 8 days of heat exposure. Plasma insulin level increased on and after day 4 of heat exposure. However, plasma cortisol and glucose levels maintained declined levels throughout the heat days.