MPB70 and MPB83 are similar but clearly distinct proteins. MPB70 is a typical secreted protein while the mpb83 and mpt83 genes contain a typical lipoprotein consensus element absent in mpb70. We show here that 26-kD MPB83 behaves as a lipoprotein upon detergent extraction and that the MPB70/MPB83 pair can be used as marker proteins for characterization of protein localization in relation to the mycobacterial cell.