The study was conducted to assess the influence of varying temperature humidity index (THI) prevalent in central midlands of Kerala on the plasma volume of castrated crossbred cattle calves and buffalo calves. The temperature humidity index varied from 76.5 to 82.0 throughout the year. No significant correlation was observed between temperature humidity index and rectal temperature (r = 0.409) in crossbred cattle calves and (r = 0.258) in buffalo calves at P<0.01 level. A positive correlation was observed between THI and plasma volume of crossbred cattle calves (r = 0.913) and plasma volume of buffalo calves (r = 0.914) at P<0.01 level.