1. Various blood indices in the Panamint kangaroo rat revealed seasonal fluctuations. The red blood cell count during winter and summer averaged 7.2 +/- 1.0 X 10(6) and 9.2 +/- 0.2 X 10(6)/mm3 respectively. 2. The mean cell hemoglobin during winter and summer averaged 25 +/- 10.8 pg and 18.6 +/- 3.7 pg respectively. 3. These fluctuations may reveal a rapid rate of red blood cell destruction during winter in combination with a change in diet, concomitant to this, is an increase in mean cell hemoglobin of the surviving red blood cells.