In rats exposed to a mixture of nitric oxides (NO -- 0.62 mg/m3, NO -- 0.60 mg/m3) and chlorine (1.02 mg/m3), for 12 weeks, a series of changes in peripheral blood have been found. In the erythrocytic system, a decrease in haemoglobin concentration in blood and mean haemoglobin concentration in erythrocytes, and increase in ALA-D dehydratase activity have been revealed. In the leukocytic system, lymphocytopenia has been found associated with a reduction in the number of lymphocytes, both beta-glucuronidase-positive and beta-glucuronidase-negative, as well as impaired lysosomes in lymphocytes, which is proved by a decrease in the number of lymphocytes with granular cytochemical reaction on beta-glucuronidase (BG) with a simultaneous increase in the number of lymphocytes with granular-diffusive and diffusive cytochemical reaction to BG. In neutrophils only a decrease in BG activity has been observed. The obtained results demonstrate that the mixture of nitric oxides and chlorine of a relatively low concentration exhibits toxic effects mainly on the lymphocytic and erythrocytic systems.