In the study, a total of 18 merino rams which were at the same age. similar body weight and healthy were used. The levels of thyroid hormone were measured in blood serum, ruminal pH and protozoa counl were determined and the species of protozoon were identified in rumen contents at different environmental temperatures in the dif· ferent seasons. The levels of blood serum total thyroxin and lolal triiodothyronine, ruminal pH and protozoa count were found to be lower amounts in the animals at 23.T'C and 20.0 % relative humidity (RH), when compared to the same values of the rams at 3.2"C and 63.3 % RH. The percentages of the protozoon species did not significantly aiter depended on the environmental temperatures in the experiment.