The inhibitory effect of sodium saccharin in concentrations of 10-5-10-2 M was tested on glycolytic enzymes involved in phosphate transfer in cell-free extracts of S. mutans NCTC 10449. In the presence of 10-2 M sodium saccharin, hexokinase, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate mutase, pyruvate kinase, 3-phosphoglycerate kinase and phosphofructokinase were inhibited 58, 45 .apprx. 16, 12, 3 and 1.4%, respectively. NaCl (10-3-10-2 M) produced little inhibition of the glycolytic enzymes tested. [These results may have relevance to the previously noted antibacterial and anticaries effects of saccharin.].