Violation of the functioning of the organs of the immune system, both in humans and in animals, is due to the influence of unfavorable factors of natural and anthropogenic origin on the body, as well as infectious diseases of various etiologies. The article discusses changes in the architectonics of parenchymal organs of white laboratory rats after exposure to the drug interferon lambda on the background of cyclophosphamide (CF). It was found that modeling of immunosuppression through the use of CF led to a decrease in the number of lymphoid cells and the appearance of foci of accumulation of blast cells and megakaryocytes, which indicates a lesion of lymphoid and hematopoietic tissues. In addition, an immunosuppressive effect on the spleen was revealed, the mass coefficient of which in the group with the use of CF was increased 3.53 times, in the group with the simultaneous use of CF and the drug interferon lambda – 2.75 times relative to the control group. There was also a decrease in the mass coefficient of the thymus by 47.6-50.0% in the same groups, which can be regarded as damage to the organs of the immune system. The negative effect of CF on the spleen was confirmed by histological examination. Thus, when inducing immunosuppression, the loss of white pulp was 73.0-77.5% relative to the group of control animals, which is 20.0% higher than in rats treated with interferon lambda, which may indicate a positive immunotropic effect of the drug under study. In addition, no significant morphological changes were detected when the body of healthy rats was exposed to interferon lambda in the studied organs, the morphological picture is similar to that of intact animals, which may indicate the safety of its use to animals.