Specific pathogen-free guinea pigs were maintained on purifieddiets low in protein (LP-10% ovalbumin; 50 ppm Zn); low in zinc (LZ-30% ovalbumin; <5 ppm Zn) or control (C-30% ovalbumin; 50 ppm Zn). Half of the animals in each diet group were vaccinated with viable Mycobacterium bovis BCG. Four and five weeks post-vaccination and diet initiation, guinea pigs from each of the 6 diet × vaccination groups were challenged with 10 3 viable Listeria monocytogenes per animal by the respiratory route and sacrificed four days later. Low protein guinea pigs demonstrated weight loss and reduced serum albumin levels. Low zinc animals were growth-retarded and had reduced plasma Zn levels. Neither LZ nor LP guinea pigs developed significant tuberculin reactions post-vaccination at either sacrifice interval. Non-specific acquired resistance against L. monocytogenes was enhanced in LP and LZ animals at 4 wks post- M. bovis BCG vaccination but not at the 5 wk interval. The anti-listeria resistance was most pronounced in the liver and spleen. While M. bovis BCG-vaccinated LP and LZ guinea pigs were incapable of expressing tuberculin hypersensitivity, they did develop a significant non-specific anti-listeria resistance.