Human immunodeficiency virus (HIV) type 1-infected persons with newly diagnosed Mycobacterium avium complex (MAC) bacteremia were enrolled in an 8-week study to determine whether treatment of MAC infection is associated with decreases in plasma tumor necrosis factor (TNF)-alpha levels. Blood specimens were obtained for quantitative MAC cultures and to determine plasma levels of HIV RNA, TNF-alpha, and other proinflammatory cytokines. MAC levels decreased by 1.75 log at week 4 (P=.008) and by 2.48 log at week 8 (P=.001). Plasma TNF-alpha decreased by 0.15 log at week 4 (P=.042) and by 0. 40 log at week 8 (P=.027). Plasma interleukin (IL)-6 decreased by 0. 56 log at week 8 (P=.039). There were nonsignificant trends (P<.10) for plasma levels of IL-1beta and HIV RNA to decrease at week 8. Nonsignificant decreases in plasma levels of TNF-alpha, IL-1beta, IL-6, and HIV RNA were also seen in those individuals who remained on stable antiretroviral therapy throughout the 8 weeks of the study.