In order to determine the effect of cyclical temperature fluctuations on thermal comfort, 804 subjects were exposed to various basal temperatures (64, 67, 73, 79 and 85°FET) which fluctuated at different amplitudes, A, (2, 4, 6, 8 and 10°F) at rates of 2, 4, 6, and 8°F/h. From their responses, equations were developed which enabled the prediction of the thermal sensation votes at the high and low points of the cycle both when the temperatures were increasing and decreasing from the basal condition. The results showed for humans engaged in near-sedentary activities while wearing light clothing, if the temperature conditions for comfort are met, the thermal environment will be acceptable if (a) the rate of change does not exceed 6°F/h (3.3°C/h) and (b) the peak-to-peak amplitude is equal or less than 6°F or +3°F (3.3°C or +1.6°C). The conditions will be unacceptable both in and out of the comfort envelope at temperatures which (a) fluctuate at rates greater than 6°F/h (3.3°C/h) or (b) have peak-to-peak amplitudes which are greater than 6°F or +3°F (3.3°C or +1.6°C). The equations were also used to predict the thermal sensations under ramp conditions. The most comfortable ascending ramp condition is when the basal temperature is increasing from between 70°F and 74°F at the rate of 1°F/h. The most comfortable decreasing ramp conditions is when the basal temperature is falling from between 78°F and 84°F at the rate of 1°F/h.