Bird (chick) embryonic development takes place within the egg ? in ovo, outside its mother's body, making the embryo readily accessible to intervention, through the window which is cut in the eggshell. This fact was initially used for elaboration of in ovo embryo vaccination technology. Advances in animal biotechnology suggest several novel approaches that may be applied to in ovo technology, including for example: stimulation of beneficial bacterial profile in the colon of chicken, stimulation of immunological response, stimulation of embryonic development, theratogenic effects testing, selection for sexual phenotype, injection of genetically modified cells, etc. The use of feed additions such as prebiotics and probiotics or their combination- synbiotics influences health and chicken performance. Their administration in ovo could have an advantageous impact on an early development of immunological system in broiler chickens. In this overview, the new possibilities for practical use of the above-mentioned additions administrated by in ovo technology were presented.