PROBLEM: To examine the capacity of sperm cells from fertile and infertile men to secrete interleukin (IL)-6, and the involvement of serum factors and lipopolysaccharide (LPS) in the regulation of IL-6 and IL-1 production by sperm cells. METHODS: Swim-up sperm cells from fertile (donors) and oligoteratoasthenospermic (OTA)-infertile men were incubated with or without 5% fetal calf serum (FCS) and LPS (10 μg/mL) for 2–24 hr. After incubation, IL-6 and IL-1 bioactivities were measured in supernatants and lysates by specific bioassays (B9 cell proliferation assay and 1A-5 system, respectively). RESULTS: IL-6- and IL-1-like activities were observed to be produced by swim-up sperm cells from both study groups. Stimulation of swim-up sperm cells with either LPS or FCS or both together did not affect their capacity to produce IL-1. However, LPS, but not serum increased the secretion levels of IL-6 by swim-up sperm cells. CONCLUSIONS: Swim-up sperm cells from both study groups constitutively produce IL-6 and IL-1, and serum components did not affect this capacity. However, LPS was shown to increase the capacity of swim-up sperm cells of both study groups to secrete IL-6, but not IL-1. Cytokines may be involved in the physiology and pathophysiology of sperm functions and, thus, may affect male fertility.