A polysaccharide isolated from Streptococcus pnemnoniae (Type n, strain R 19) was purified and analyzed. The constituent sugars were galactose, mannose and gluco-samine. The acetyl content of the polysaccharide indicated that the glucosamine was fully acetylated on the N position and that some 0-acetyl was also present. The total phosphorus content was greater than that attributable to known ribonucleic acid (RNA) and deoxyribonucleic acid (ONA) contamination. Glucosamine-N, RNA-N, and DNA-N did not account for the total N which, from the amino acid pattern, appeared to be associated with protein.