Chronic hemodialysis (HD) patients have defects in cell-mediated immunity. To investigate the mechanisms underlying this immunodeficiency, we studied the production of cytokines in peripheral blood mononuclear cells (PBMC) from HD patients. PBMC from 22 HD patients and 20 healthy controls were cultured for 48 h in the presence or absence of phytohemagglutinin (PHA), lipopolysaccharide (LPS), or tuberculin purified protein derivative (PPD). Cytokine levels were measured by enzyme-linked immunosorbent assays. Only 64% of HD patients had a positive tuberculin skin test compared to 90% of normal Japanese controls. HD patients showed a diminished proliferative response to PHA. Compared to healthy controls, stimulated PBMC from HD patients produced similar amounts of T cell-derived cytokines (interleukin-2 (IL-2) and interferon-gamma (IFN-gamma)), but greater amounts of monocyte-derived inflammatory cytokines (IL-1 beta, tumor necrosis factor-alpha (TNF-alpha), and IL-8) and a regulatory cytokine (IL-10). IL-10 production was positively correlated with IL-1 beta and TNF-alpha in healthy controls, whereas no correlation was observed in HD patients. Abnormal cytokine production by monocytes may contribute to the immunodeficiency seen in HD patients.