Quantification of mycobacteria in sputum from pulmonary tuberculosis patients has been used to evaluate patient's response to treatment since the earliest days of anti-tuberculosis chemotherapy. More recently the early bactericidal activity (EBA) of anti-tuberculosis agents, measured as the fall in viable colony forming units of Myco-bacterium tuberculosis in sputum early in therapy, has been shown to be an objective, repeatable measure of the ability of an agent to kill the metabolically active bacilli found in the sputum of patients with sputum microscopy smear-positive pulmonary tuberculosis. EBA offers an opportunity to rapidly demonstrate that a new agent has a detectable anti-tuberculosis effect in a relatively small number of patients, what the most appropriate dose is to take forward to more extensive clinical trials and allows the study of the relationship between pharmacokinetics and bactericidal activity and toxicity of the relevant agent.