Use of a novel adjuvant (Immunoboost) to enhance antibody titers in response to a commercial vaccine (Lysigin) against Staphylococcus aureus mastitis in dairy heifers was evaluated in a 2-phase trial. Heifers 5 to 12 mo of age were used in both study phases and blood samples were collected weekly for processing (ELISA) to determine anti-S. aureus antibody levels; baseline titers before each phase did not exceed 1:1600. In phase 1, hyper-immunization with Lysigin to enhance the level and duration of titers did not result in titers that consistently exceeded conventional immunization. In phase 2, anti-S. aureus titers in heifers immunized with Lysigin + 2 mL Immunoboost tended to be elevated (P = 0.10) over those of heifers immunized conventionally with Lysigin alone by d 7 after initial immunization, a trend that continued through d 14. By d 21, titers in the Immunoboost group were elevated (P = 0.05) over conventional vaccinates and remained significantly elevated through d 35, returning to baseline by d 42. After receiving booster injections on d 42, the Immunoboost group experienced an increase (P = 0.05) in titers over conventional vaccinates on d 49 of the trial, and titers remained significantly elevated through d 63. Titers in the Immunoboost group remained elevated over conventional vaccinates through d 84 of the trial, but the difference was not significant, and titers in both groups were approaching baseline values. Findings suggest that Immunoboost is capable of enhancing the antistaphylococcal titer response to the commercial vaccine Lysigin, albeit in the short term. These studies indicate that continued study of using immunization to control S. aureus mastitis in dairy heifers is justified.