We conducted a 12-month prospective study comparing two approaches to the detection of Mycobacterium avium in the blood of human immunodeficiency virus type 1-infected patients, namely, a lytic centrifugation system combined with Middlebrook solid culture medium (the conventional procedure) and the nonradiometric BACTEC 9000 MB system. Species identification relied on 16S rRNA probe hybridization and cell wall fatty acids chromatography. M. avium was isolated in 17 of 345 (5%) blood specimens by the BACTEC 9000 MB automated system and in 14 of 345 (4%) blood specimens by the conventional procedure (nonsignificant, ² test). Detection time was 16 ± 6 days by the BACTEC 9000 MB automated system and 27 ± 3 days by the conventional procedure (P < 0.001, Student t test). Non-M. avium mycobacteria were not recovered during the study period. Contamination rate was 8% (30 specimens) by the BACTEC 9000 MB system and 0% by the conventional procedure, indicating the necessity of using an antibiotic mixture (PANTA, consisting of polymyxin B, amphotericin B, nalidixic acid, trimethoprim, and azlocillin). Working time was 1 min 30 s by the BACTEC 9000 MB system and 8 min by the conventional procedure, which was 1.8 times more expensive than the BACTEC system. Use of the BACTEC 9000 MB system increased the sensitivity of M. avium detection and reduced detection time in blood culture.