The purpose of the study was to examine of bacteria present in chicken embryos and newly hatched chicks. The bacteria were determined quantitatively in caecal contents, liver and yolk sac of 25 embryos at 18 day of incubation, 25 embryos at 20 day incubation, and 25 newly hatched chicks. Gram-positive cocci belonging to the Enterococcus genus dominated in all samples examined and their population number amounted from 10² to 10⁶ CFU/g in caecal contents, 10²-10⁴ CFU/g in yolk sac, and 10³ CFU/g in liver. Other bacteria present in some samples were: Staphylococcus sp. 10²-10⁴ CFU/g, E. coli 10⁶ CFU/g, C. tertium 10⁵ CFU/g, Klebsiella sp. 10⁴ CFU/g, and Enterobacter sp. 10² CFU/g. The results obtained indicate that the profile of gut microflora becomes more differentiated and their population number of particular groups higher with the age of embryos. Moreover, potentially pathogenic bacteria, including anaerobic Clostridium tertium may be isolated already during hatching period, suggesting the possibility of infection of embryos and newly hatched chicks.