Effects of immunomodulators and ionizing radiation on 5-nucleotidase activity in macrophages of peritoneal exudate are governed by the mirror "symmetry principle, similar to that determining the effects of Yersinia enterocolitica on the lymphocyte blastogenesis of inbred mouse splenocytes. The control values are particularly important in comparative experiments. We investigated the relationship between the IM effect and the initial state of the immune system in intact animals at the moment of drug injection and at the moment of investigation of the effect of immunomodulator (IM). We investigated the conformity of IM response to Wilder's law and the mirror symmetry principle (MSP). Wilder's law reflects the relationship between changes in the studied parameter and its initial value at the moment of exposure. According to this regularity, a function is the less stimulated and easier suppressed, the stronger it is activated at the moment of exposure, and vice versa [4]. Previously we demonstrated a relationship between IM effect and the level of the studied parameter in control animals at the moment of in~.~stigation and proved that IM reactions obey MSP i2]. The MSP states that the direction and magnitude of IM effect on a parameter inversely depends on the level of this parameter in control animals at the moment of investigation.