The aim of the present study was to establish whether growth hormone (GH) treatment in vivo affects pro-inflammatory cytokine production by resting or in vitro, activated, cultured, peripheral blood mononuclear cells (PBMC) from children with complete growth hormone deficiency (GHD). We evaluated 11, pre-pubertal children (6 males and 5 females) with GHD, aged between 6 and 14 years, and 9, age- and sex-matched healthy subjects were studied as controls (CTRLs). Freshly isolated PBMC were cultured for 4 or 24 h in X-VIVO medium in the presence or absence of 0.01 microg/mL lipopolysaccharide for the determination of TNF-alpha and IL-6 production; alternatively, cells were incubated 24 h in X-VIVO medium with or without 25 microg/mL Concanavalin A for IFN-gamma production. Cytokines were measured in the cell supernatants by enzyme-linked immunosorbent assay kits. The results of the present study provide evidence that spontaneous and/or mitogen-induced, in vitro PBMC production of pro-inflammatory cytokines is lower in GHD children than in healthy, age-matched individuals (p<0.05 by the Mann-Whitney U-test). After 3 months of GH therapy, cytokine production was significantly (p<0.05 by the Wilcoxon test) increased, but was still lower than in healthy controls. It is reasonable to speculate that severe GH deficiency can cause alterations in the pro-inflammatory cytokine-induced immune response in humans, and that GH treatment can ameliorate this important immunological function.