Capsular polysaccharides (CPs) from Streeptococcus pneumoniae were examined for the ability to induce secretory responses in a pure population of peritoneal macrophages. The highly purified CPs were able to affect the macrophage, ie, secretion of tumor necrosis factor-alpha (TNF-$alpha$) and nitrite. As after stimulation with CPs, secretion of TNF-u induced by these CPs reached its maximum within the first few hours of the interaction, while secretion of nitrite was increased with time. In addition, production of TNF-$alpha$ and nitrite was increased in a dose-dependent manner. In the presence of indomethacin, CP-stimulated TNF-$alpha$ production was not altered. In contrast, LPS with indomethacin stimulated 24.5% more TNF-$alpha$ than LPS alone, suggesting that the intracellular signaling processes for TNF production are differentially stimulated by CP and LPS. The results demonstrate that CPs are potent inducer of macrophage secretory activities.