MPC measurements were obtained with M. tuberculosis for many of the traditional anti-tuberculosis agents. In the second column we list maximal serum concentrations taken from the literature (based on recommended doses). In almost all cases MPC is above the maximal serum concentration (ratio greater than 1), meaning that it is not possible to exceed MPC with these compounds and this organism. These data provide the framework for the empirical observation that anti-tuberculosis agents need to be used in combination to restrict the development of resistance. Two compounds that have ratios below 1 are C-8-methoxy fluoroquinolones. These data illustrate the special mutant-restricting property of moxifloxacin and gatifloxacin. However, they should not be taken as meaning that the compounds are especially good against tuberculosis, since the data do not address the ability of the compounds to kill the organism.