Polymerase chain reaction (PCR) has been widely investigated for the diagnosis of tuberculosis. However, before this technique is applied on clinical samples, it needs to be well standardized. We describe the use of McFarland nephelometer, a very simple approach to determine microorganism concentration in solution, for PCR standardization and DNA quantitation, using Mycobacterium tuberculosis as a model. Tuberculosis is an extremely important disease for the public health system in developing countries and, with the advent of AIDS, it has also become an important public health problem in developed countries. Using Mycobacterium tuberculosis as a research model, we were able to detect 3 M. tuberculosis genomes using the McFarland nephelometer to assess mycobacterial concentration. We have shown here that McFarland nephelometer is an easy and reliable procedure to determine PCR sensitivity at lower costs.