In the first part of our work (1) it was found that the cultivation of blood of sensitized people and animals with specific allergen (AI) caused the phenomenon of specific inhibition stimulated luminol-dependent chemiluminescence of leukocytes (PhSISCL). In the current study the mechanism of this inhibition was investigated. It was revealed that PhSISCL resulted from the direct influence of AI on polymorphonuclear leukocytes (PMNL). The activity of NADPH-dependent oxidase was established by the Wymann M. et al. method (2). It was determined that the values of chemiluminescence (CL) for the cultivation of sensitized rabbit blood with specific AI did not differ from the control. This demonstrated that the activity of NADPH-oxidase was not inhibited. On these grounds it is possible to assume that PhSISCL is connected to either the inhibition of myeloperoxidase (MPO) activity or to a release of this ferment from PMNL during cultivation. The latter was specifically investigated and was not confirmed.