Serotyping was performed on Mycobacterium avium isolates from 40 AIDS patients from 5 geographic sites: Boston (17 patients), New Hampshire (4 patients), Finland (12 patients), Trinidad (3 patients), and Kenya (4 patients). Serovars were similar from the five sites. Serovars 4 and 8 were the most common. In addition, minimal inhibitory concentrations to 8 antimicrobial agents were determined for 31 of these isolates and for 21 additional patient isolates from these sites. Minimal inhibitory concentration90 values for clarithromycin, azithromycin, clofazimine, amikacin, ethambutol, ciprofloxacin, sparfloxacin, and rifabutin were similar for isolates from the five geographic sites. Antimicrobial susceptibility patterns did not differ by serovar.