Reactive oxygen species production has been demonstrated to impair sperm function. We have noted the potential for the cytokines IL-1 alpha, IL-1 beta, and TNF alpha to stimulate reactive oxygen species production by fertile donor sperm at levels that are consistent with the levels of IL-1 occurring in human seminal plasma. Reactive oxygen species-related sperm membrane peroxidation may be one mechanism by which cytokines can exert a detrimental effect on male fertility. This study suggests a new mechanism by which cell-mediated immunological male infertility may occur.