An experiment was conducted with rats to determine whether silicon deprivation affects the inflammatory response to the injection of type II collagen, and to compare the effectiveness of the organic complex arginine silicate inositol (ASI) with inorganic silicon (NaSiO(3)) in mitigating any observed change in response. Dark Agouti rats were fed a ground corn-casein-safflower-based diet containing about 2.8 mg Si/kg. The experimental variables were supplemental 0 and 35 mg Si/kg as either ASI or NaSiO3. After five weeks on their respective treatments, each rat was injected with type II collagen and euthanized four weeks later. Urine was collected before injection during week five and week nine before euthanasia. The silicon-supplemented rats generally exhibited a more marked inflammatory response than the silicon-deprived rats. The circulating number of lymphocytes was higher (p<0.003) and number of neutrophils was lower (p<0.008) in silicon-deprived than silicon-supplemented rats. ASI and NaSiO3 were about equally effective in enhancing these changes. Post-injection of tibial release of prostaglandin E(2) (PGE(2)) (p<0.04), urinary excretion of magnesium (p<0.03) and deoxypyridinoline (p<0.009), and plasma osteopontin (p<0.009), magnesium (p<0.0007) and copper (p<0.004) were higher in silicon-supplemented than silicon-deprived rats. The increases in plasma magnesium (Si x sex, p<0.04) and copper (Si x sex, p<0.02) were more marked in male than female rats. One but not the other silicon supplement when compared to silicon deprivation significantly affected the tibial release of PGE(2), and plasma copper and iron concentrations. However, with the exception of the pre-injection urinary excretion of helical peptide, no other of the variables determined was significantly different between rats fed ASI and those fed NaSiO3. The findings suggest that, in rodents, physiological amounts of silicon promote the immune response, sex may influence the response to dietary silicon, and that both organic silicon complexes and inorganic silicon are similarly effective in preventing changes in inflammation induced by silicon deprivation.