Healthy volunteers were randomized to receive percutaneous or intradermal bacille Calmette-Guérin (BCG) vaccination. Delayed-type hypersensitivity (DTH) to tuberculin, as well as proliferative and interferon-gamma responses in peripheral blood mononuclear cells stimulated by whole cell lysates and culture filtrates of Mycobacterium tuberculosis and Mycobacterium avium-intracellulare, were compared before and after vaccination. Positive DTH reactions were detected in 83% of intradermal and 40% of percutaneous BCG recipients 3 months after vaccination (P < .004). M. tuberculosis-specific proliferation was increased after intradermal BCG (P < .01) but not after percutaneous BCG compared with prevaccination responses. In addition, M. tuberculosis-specific interferon-gamma production was increased after intradermal BCG compared with both prevaccination responses (P < .04) and those measured after percutaneous BCG (P < .05). Predominant immune responses stimulated by BCG were directed against antigens present in mycobacterial whole cell lysate. These results indicate that the BCG vaccination route can affect both in vivo and in vitro immune responses.