This guideline addresses the evaluation of new antimycobacterial drugs in the treatment and prevention (secondary prophylaxis) of infection by M. tuberculosis. Patients may be enrolled in clinical trials on the basis of clinical and/or microbiological criteria. A therapeutic regimen will likely include a combination of drugs; a randomized, active-control, comparative clinical trial is recommended. If appropriate samples can be obtained for culture during follow-up without placing the patient at unwarranted risk, the assessment of microbiological outcome is paramount. Prophylaxis will probably require a single drug, and a similar study design is preferred.