Disclosed is a new and emerging serotype of Streptococcus pneumoniae designated serotype 6D, 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->;4) ribitol (5->;phosphate. This new serotype may be included in pneumococcal vaccines.