The details of how and why TDM should be performed have been published previously.2–4 More recently, larger clinical trials have noted that, in certain situations, low serum concentrations of the TB drugs are associated with worse treatment outcomes.5–6 Although not designed as TDM studies, they do point out that some minimum drug exposure is required for the drugs to be effective. Further, they show that certain patients, such as those with HIV, are particularly susceptible to adverse outcomes should their drug exposures be too low. As a first step, the Centers for Disease Control and Prevention no longer recommends intermittent treatment regimens for HIV-positive patients.7It also may be time to consider higher initial doses for certain TB drugs, at least for selected patient populations, although such dose changes may require additional clinical trials for validation. Short of revising the guidelines, TDM performed early during treatment allows for timely dose adjustments that generally can overcome poor drug absorption. If TDM is performed early in treatment, poor clinical outcomes may be avoided. Clinical judgment is required to determine the patients to whom this approach should be applied. It has been the practice at certain centers, such as National Jewish Medical and Research Center and the A.G. Holley State Hospital (Lantana, FL) to perform TDM for nearly all TB patients. This reflects the difficult clinical problems facing many of these patients, including extensive drug resistance or multiple concurrent medical problems.8–9 Other centers, such as the Texas Center for Infectious Diseases (San Antonio, TX), San Diego TB Control (San Diego, CA), the Orange County Health Department (Westminster, CA), and Hennepin County Medical Center (Minneapolis, MN), use TDM in a substantial cohort of their TB patients. Like Li and colleagues, who are from New York City, it is likely that clinicians and laboratory investigators at these centers also would be willing to share their experiences with those at other centers who were interested in getting started with TB drug TDM.