The newly recognized species Mycobacterium genavense causes disseminated infections in AIDS patients, but its prevalence is difficult to assess because of its inability to grow on standard solid media. For the same reason, very little is known about the phenotypic traits of its isolates. We report here the results of our studies on two such strains isolated from AIDS patients and subcultured on a non-standard solid medium. Besides several features conventionally explored for mycobacterial speciation, we tested the isolates for 19 enzymatic activities and determined their mycolic acids profiles by means of high performance liquid chromatography. We also compare our findings with the scanty literature data on the laboratory characteristic and antimicrobial susceptibility of M. genavense.