The term "proteomics" describes the technologies collectively used to define the protein complement of the genome or "proteome" (1,2). The recent growth of this discipline is reflected in the many review articles available (3-7). In addition to describing all the proteins encoded by the genome, the proteome also provides information on protein expression under defined conditions or at a particular point in time, the occurrence of posttranslational modifications, and the distribution of proteins within the cell. Proteomics, most commonly, combines the technique of two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), developed simultaneously but independently by O'Farrell (8) and Klose (9) in 1975, with image analysis, protein mass spectrometry, and database searching to assign protein identities to spots from 2D gels. Recent advances in the sensitivity and accuracy of protein mass spectrometry (3,10-12), coupled with availability of the complete genome sequence of two strains of Mycobacterium tuberculosis (13, http://www.tigr.org/), have facilitated the study of the proteome of this organism. Under defined growth conditions, this may help to elucidate the mechanism of M. tuberculosis survival within the host.