In persons with human immunodeficiency virus (HIV) infection and/or acquired immunodeficiency syndrome (AIDS), the immune system becomes dysfunctional in many ways. There is both immunodeficiency due to the loss of CD4-positive T helper cells and hyperactivity as a result of B-cell activation. Likewise, both decreases and increases are seen in the production and/or activity of cytokines. Cytokine changes in HIV infection have been assessed by a variety of techniques, ranging from determination of cytokine gene expression at the mRNA level to secretion of cytokine proteins in vivo and in vitro. Changes in cytokine levels in HIV-infected persons can affect the function of the immune system, and have the potential to directly impact the course of HIV disease by enhancing or suppressing HIV replication. In particular, the balance between the pro-inflammatory cytokines interleukin (IL)-1, IL-6, and tumor necrosis factor-alpha, which up-regulate HIV expression, and IL-10, which can act both as an anti-inflammatory cytokine and a B-cell stimulatory factor, may play an important role in the progression to AIDS. In light of its ability to suppress the production of pro-inflammatory cytokines and, under some conditions, suppress HIV replication, increased IL-10 may be viewed as beneficial in slowing HIV disease progression. However, an association between increased IL-10 and the development of AIDS-associated B-cell lymphoma highlights the bifunctional nature of IL-10 as both an anti-inflammatory and B-cell-stimulatory cytokine that could have beneficial and detrimental effects on the course of HIV infection and AIDS.