However, the lungs of mice inoculated with M. tuberculosis or M. canettii exhibited means of 0.033 nodules mm22 and 0.3202 nodules mm22, respectively. For the spleen, mice challenged with M. tuberculosis and M. canettii showed means of 0.0332 nodules mm22 and 0.157 nodules mm22, respectively. For the liver, only mice challenged with M. canettii showed nodules, with a mean of 0.087 nodules mm22. For mice challenged with M. bovis, all tissues were free of nodules. Likewise, tissues collected from negative controls remained free of nodules. At 90 days postinfection the organs collected from negative control mice remained sterile whereas the mycobacterial load in the liver was 26103±0.56103 c.f.u. ml21 for all mycobacteria; in the spleen it was of 8.46104±4.456104 c.f.u. ml21 for M. tuberculosis, 4.966104±1.216104 c.f.u. ml21 for M. bovis and 105 c.f.u. ml21±4.086104 for M. canettii; in the lungs it was of 3.296103±3.146103 c.f.u. ml21 for M. tuberculosis, 2.436103±1.386103 c.f.u. ml21 for M. bovis and 6.566104±1.766104 c.f.u. ml21 for M. canettii.