The location of injection and vaccine deposition in ovo is known to be critical to the efficacy of Marek's disease (MD) vaccine protection against MD viral challenge. Vaccine deposition into the amniotic sac or a s.c. or i.m. site of the embryo is required for MD vaccine efficacy. Vaccine deposition into the air cell or allantoic fluid results in chicks that are not adequately protected against subsequent MD viral challenge. A study was conducted in 2 commercial broiler hatcheries to evaluate the ability of 2 in ovo injection systems, the Embrex Inovoject system (Pfizer Poultry Health, Research Triangle Park, NC) and the Intelliject system (Avitech, Salisbury, MD; distributed by Merial Ltd., Gainesville, GA) to deliver a vaccine approved for use in ovo accurately and properly. A standard MD vaccine diluent mixed with a protein-staining dye was delivered through each machine to simulate in ovo vaccination. The location of the dye within the egg determined whether the vaccine was delivered correctly. Each egg was also evaluated for normal embryo development (normal eggs). Correct vaccine delivery included eggs in which the vaccine was injected into the amniotic sac or into s.c. or i.m. regions of the embryo. Incorrect vaccine delivery was defined as delivery into the air cell; allantoic sac; any combinations including air cell or allantois; the abdominal, cranial, orbital, or thoracic cavities of the embryo; or no vaccine delivery at all. In hatchery 1 (Chick Master, Newton, MS) 1,171 normal eggs were processed through the Inovoject system and 1,138 eggs were processed by the Intelliject system. The Inovoject system correctly vaccinated 94.62% of the normal eggs as compared with 61.16% delivery accuracy of normal eggs with the Intelliject system. In hatchery 2 (Jamesway Super J, Magee, MS) 926 normal eggs were processed by the Inovoject system and 910 normal eggs were processed by the Intelliject system. The Inovoject system correctly vaccinated 91.04% of the normal eggs, whereas the Intelliject system correctly vaccinated 71.98% of the normal eggs. The results of this study clearly demonstrate that the Inovoject system accurately delivered in ovo vaccine at a significantly higher rate than the Intelliject system.