Dietary fibers, including pectin, have been shown to exert a favorable effect on a wide spectrum of pathological conditions. Their positive influence on human health is explained by their anti-oxidative, hypocholesterolemic and anti-cancerous effects. However, little has been reported about their activity on the immune system. Therefore, the present study was undertaken to examine the effect of citrus pectin (CP) on cytokine production by human peripheral blood cells (PBMC). PBMC were incubated without or with CP at different degrees of esterification (DE) (approximately 30, approximately 60 and approximately 90% esterified pectin, assigned as DE30, DE60 and DE90, respectively) for detection of IL-1 beta, IL-1 ra, TNFalpha, IL-6 and IL-10 secretion. Incubation with DE60 and DE90 induced a dose-dependent inhibition of the pro-inflammatory cytokine IL-1 beta secretion, whereas D30 did not affect this function. However, CP at all three esterification degrees did not alter the secretion of the additional pro-inflammatory cytokines examined, i.e. TNFalpha and IL-6. Conversely, CP at DE60 and DE90 caused a dose-dependent increased secretion of the anti-inflammatory cytokines IL-1 ra and IL-10, whereas D30 did not affect the production of IL-1 ra and decreased that of IL-10. The findings indicate that CP possesses the capacity to exert an immunomodulatory response in human PBMC which may have a favorable effect on human health.