Using the quantitative immunohistochemistry, the immunomodulatory effect of different types of stressors (physical and psychoemotional) on the thymus of growing experimental animals was assessed. Sprague-Dawley rats aged 21 day were exposed either to physical (water immersion) or emotional «expectation» stress for 5 hours daily during 7 consecutive days. After the final exposure to stress, animals were sacrificed, thymus was obtained for weighting and was processed for routine histology and immunohistochemistry (CD3, CD8, ED1, PCNA) with subsequent automatic image analysis. The finding obtained have demonstrated severe accidental thymic involution in both groups of experimental animals, which was more prominent under the effect of the physical stressor as compared to «purely» psychoemotional stressor. The major factors of poststress thymic hypoplasia were the increased apoptosis of the cortical thymocytes and inhibition of their proliferation, but not their increased transport to peripheral immune organs.