To determine the effects of acute plasma volume expansion and heat exposure on the periodic oscillations of selected hormones, two doses of albumin were administered intravenously followed by exposure to heat stress (37°C, 25–30% RH). Plasma volume was previously established by a dye dilution technique using indocyanine green. During heat exposure blood samples were taken from antecubital catheters at 1, 3, 6, 9, 12, and 24 hours following completion of albumin or saline (control) infusion, and the plasma analyzed. No significant effects of heat stress or albumin administration were noted on circulating cortisol concentrations or on the diurnal/nocturnal periodicity of cortisol and aldosterone levels. There did occur a significant reduction in plasma levels of aldosterone as a result of albumin‐induced plasma volume expansion. We concluded that the duration and intensity of heat stress used in these studies had no effects on plasma hormonal levels and periodicities, but plasma volume expansion elicited a significant decrement in aldosterone concentrations.