Ten strains of Streptococcus mutans, representing four serological groups, have been grown in chemically defined media. For anaerobic growth, one of the strains required the following organic compounds: glucose, cysteine (or thioglycolic acid), biotin, p-aminobenzoic acid, thiamine, riboflavin, pyridoxine, pantothenic acid and nicotinic acid. Except for this vitamin requirement, the organism could use ammonia as the sole source of nitrogen for growth. In aerobic culture, uracil and one of the amino acids, glutamine, glutamic acid, asparagine or aspartic acid, had to be included in the medium for growth of the organism.