The authors of this Comment article discuss the growing problem of multi-drug and extensively drug-resistant tuberculosis (MDR and XDR, respectively) and why they believe moxifloxacin should be reserved as a second-line treatment.  They use this case to emphasize the importance of the pressing question for researchers, policy makers and clinicians involved in this area of practice - should new tuberculosis drugs be prioritised for the treatment of drug-susceptible or drug-resistant tuberculosis?