The objective of this Investigation was to evaluate the effects of dietary probiotics on blood and immunological parameters in broiler chickens. A total of 300 broiler chickens of 21 days of age were distributed in metabolic cages according to a completely randomized experimental design in 5 treatments: Control, with probioticsSaccharomyces cerevisiae, Lactobacillus acidophilus, Bacillus subtilis and mixture of the three probiotics mentioned with 4 replicates of 15 birds each. Erythrocyte count, haematocrit, haemoglobin, total re-counting of leukocytes, heterophils, lymphocytes, eosinophils, basophils, monocytes, platelets and antibody titers for Newcastle, Bronchitis and Gumboro were determined. The average results were: haematocrit 34.8%; haemoglobin 11.6 g/dL; average corpuscular volume 160.2; average corpuscular haemoglobin concentration 33.2 g/dL; erythrocytes 2.2x106 μL; leukocytes 25.1x103 μL; relative values of lymphocytes 44.1%; heterophiles 43%; monocytes 3.5%; eosinophils 3.1%, and basophils 0.1%. Results are found in the normal ranges, showing variations attributed to probiotics added in the diet. Therefore, further research is needed on the haematological parameters of birds.