The subcutaneous, intradermal, and pulmonary inflammatory lesions induced in mice by viable Mycobacterium bovis (BCG) with no glycolipid cord factor (CF) on the outer cell wall (delipidated BCG, dBCG) was drastically different from that induced by inoculation with intact bacteria. The reaction caused by dBCG was of an acute nature: the cells making up the inflammatory infiltrate exhibited polymorphonuclear-like (PMNs) morphologic characteristics, there was a decrease on delayed hypersensitivity response, and the lesion was resolved around the 16th day after inoculation. Complete disappearance of viable organisms from the lungs, liver, and spleen of these animals occurred in parallel with the dissipation of the dBCG-induced inflammatory infiltrate, showing that CF plays an important role in the host-parasite relationship that takes place in infections caused by mycobacteria. In addition, when deprived of this glycolipid component, bacilli lose their immunostimulant ability.