Disclosed is a new and emerging serotype of Streptococcus pneumoniae designated serotype 6C, and assays and monoclonal antibodies useful in identifying same. Also disclosed is a novel pneumococcal polysaccharide with the repeating unit {2) glucose 1 (1→3) glucose 2 (1→3) rhamnose (1→3) ribitol (5→phosphate}. This new serotype may be included in pneumococcal vaccines.