From January through July of 2000, a study was conducted to evaluate clearance, immunologic responses, and potential shedding of Brucella abortus strain RB51 (SRB51) following ballistic or subcutaneous (SQ) vaccination of 7 mo old bison (Bison bison) calves. Ten bison calves were vaccinated SQ with 1.4 x 10(10) colony-forming units (CFU) of SRB51 and five calves were inoculated SQ with sterile 0.15 M sodium chloride. An additional 10 bison calves were ballistically inoculated in the rear leg musculature with 1 x 10(10) CFU of SRB51 and five calves were ballistically inoculated with an empty Biobullet. Serologic responses were monitored at 0, 2, 4, 6, 8, 12, 18, and 24 wk using the standard tube agglutination test and a dot-blot assay. Swabs from rectal, vaginal, nasal, and ocular mucosal surfaces, and blood were obtained for culture from all bison at 2, 4, 6, and 8 weeks post-inoculation to evaluate potential shedding by vaccinated bison or persistent septicemia. The superficial cervical lymph node was biopsied in eight ballistic and eight hand vaccinated bison at 6 or 12 wk to evaluate clearance of the vaccine strain from lymphatic tissues. Lymphocyte proliferative responses to irradiated SRB51 bacteria were evaluated in peripheral blood mononuclear cells (PBMC) at 4, 6, 8, 12, 18, and 24 wk after inoculation. Serum obtained from hand or ballistically vaccinated bison demonstrated antibody responses on the dot-blot assay that were greater than control bison (saline or empty Biobullet) at 2, 4, 6, and 8 wk after vaccination. Antibody titers of ballistically vaccinated bison did not differ (P > 0.05) from hand vaccinated bison at any sampling time. Blood samples obtained from all bison at 2, 4, 6 and 8 wk after vaccination were negative for SRB51. One colony of SRB51 was recovered from the vaginal swab of one ballistically vaccinated bison at 2 wk after vaccination. All other ocular, vaginal, nasal, and rectal swabs were culture negative for SRB51. Strain RB51 was recovered from superficial cervical lymph nodes of hand and ballistic vaccinated bison at 6 (two of four and two of four bison, respectively) and 12 wk (three of four and one of four bison, respectively). Serologic tests and bacterial culture techniques failed to demonstrate infection of nonvaccinated bison. Peripheral blood mononuclear cells obtained from hand vaccinated bison had greater (P < 0.05) proliferative responses to strain RB51 bacteria when compared to PBMC from nonvaccinated and ballistically vaccinated bison. Proliferative responses of PBMC from ballistically vaccinated bison did not differ (P > 0.05) at any sampling time from proliferative responses of PBMC from control bison. Serum alpha 1-acid glycoprotein concentrations, plasma fibrinogen, and total protein concentrations were not influenced by treatments. Ballistic delivery of SRB51 did not induce adverse effects or influence clearance of the vaccine strain. There were no proliferative responses of PBMC to SRB51 in bison ballistically vaccinated with SRB51; whereas bison inoculated with SRB51 by hand injection had greater proliferative responses than control or ballistically vaccinated bison. Our study suggests that ballistic delivery may require a greater dose of SRB51 to induce cell-mediated immune responses in bison that are comparable to those induced by hand injection, and that ballistic or hand delivery of 1 x 10(10) CFU of SRB51 is safe in bison calves.