This study was carried out to determine the effect of altered dietary protein level on the antioxidant status of erythrocytes of in vivo heat exposed rats. Experiments were performed on adult (80-90 days old) male Wister strain rats, divided in six groups of five animals each. Animals were exposed to 43---PlusMinusSymbol---1 __degreesignC, ambient humidity conditions for 3 h daily for 15 days in a well maintained climatic chamber. Increased TBARS productions were found when measured in packed erythrocytes and erythrocyte membranes in both the rats fed on 18% or 6% protein diet after acute and chronic heat exposure. Supplementation of ascorbic acid to the rats fed on 18% or 6% protein diet was found to reduce the TBARS production remarkably in packed erythrocytes while it further raised the TBARS production in erythrocyte membrane in response to chronic and acute heat exposure. The liberation of alanine increased in 18% protein-fed as well as 6% protein-fed rats following chronic and acute exposure to heat. Decreased GSH content and increased membrane total thiol (-SH) content of erythrocytes were observed in both 18% protein-fed and 6% protein-fed rats. Prior supplementation of ascorbic acid was found to restore partially the GSH content of erythrocyte and to potentiate the increase in membrane total thiol (–SH) content in both adequately protein-fed and protein-restricted groups of rats.