Abstract. An experiment using 22 440 broiler chickens (Ros-308) was conducted to assess the influence of the commercial preparation Rescue Kit SL (containing Bacillus licheniformis and Bacillus subtilis, betaine, vitamins and microelements), administered in the drinking water (1g/litre) from the age of 9 to 14 days. One group, constituted by the same number of chickens, that were not given the additive, was considered as control. Performance indices were measured weekly and blood samples were collected from 14, 35 şi 50-d-old chicks for biochemical and hematological analyses. The results indicate a reduced lethality rate in experimental group 3.5%, while 3.9% (control). At the end of the production cycle (50 days) the body weight was by 50 g (P< 0,05) higher in broiler chickens from the experimental group. The preparation Rescue Kit SL induced the increase of erythrocytes, hemoglobin, total protein and glucose in blood serum, resulting from the intensification of metabolic processes. Key words: Broiler chickens; Probiotics; Hematological indices; Biochemical indices; Body weight. Rezumat. Cercetările s-au efectuat pe un lot de 22 440 pui broiler (Ros-308) cu scopul de a stabili efectul produsului comercial Rescue Kit SL (conţine Bacillus licheniformi şi Bacillus subtilis, betaină, vitamine şi microelemente), administrat cu apa de băut (1g/ litru) de la vârsta de 9 până la 14 zile. Un lot, format din acelaşi număr de pui, care nu au primit aditivul, a fost considerat martor. Săptămânal s-au determinat indicii bioproductivi, iar la vârsta de 14, 35 şi 50 de zile s-au prelevat probe de sânge pentru analize biochimice şi hematologice. Rezultatele indică o reducere a procentului letalităţii (3,5 %) în lotul experimental, pe când 3,9% (martor). La finele ciclului de producţie (50 zile) greutatea corporală a fost cu 50 g (P< 0,05) mai mare la puii din lotul experimental. Produsul Rescue Kit SL a indus o creştere a eritrocitelor, a hemoglobinei, a proteinei totale şi a glucozei în serul sangvin, fiind un rezultat al intensificării proceselor metabolice.