The purpose of this study was to establish a system that would allow rapid and reliable quantification of Mycobacterium avium complex infection with a method that was as sensitive as counting of colony-forming units but less time-consuming and safer in the laboratory. The radiometric system for quantification of mycobacteria (Bactec, Becton Dickinson, USA) which calculates growth curves, was found to be faster, safer, and as sensitive as the established method of counting colony-forming units, with a low intra-assay variation and a wide assay range. Furthermore, the calculated growth curves provided important additional information about replication characteristics of the mycobacteria.