The study carried out on a lot of 80 broiler chickens COBB-500, divided into a control group and an experimental group assessed the influence of Sel-Plex product (organic selenium) on the bioproductive indices and blood parameters. The chicks from the experimental group were administered, in addition to their basic ration, the Sel-Plex product in dose of 0,4 mg Se/1kg of feed, from one to 49 days of age. The results of investigations of clinical indices (general state, plumage, behavior, feed intake, daily weight gain, morbidity, and lethality) re-vealed the positive effect of supplementing daily rations with organic selenium on the growth and development of chickens. The lethality rate was lower in the experimental group (0 %) in comparison with the control (5 %). The body weight was 4,63 % higher compared to chickens of the control group. The dynamics of paraclinical indices (erythron, biochemical parameters, malondialdehyde content, activity of superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase in serum) show that the Sel-Plex product has beneficial effects on erythropoiesis, metabolic and antioxidant status.