Glucose metabolism in Corynebacterium glutamicum was investigated using 13C nuclear magnetic resonance (13C NMR) spectroscopy. LGlutamic acid and L-lysine producers were cultivated in medium containing [ l-13C]-or [6-13C] glucose, and the 13C NMR spectrum of the culture filtrate was measured. In each fermentation, the ratio of the contributions of the Embden-Meyerhof pathway (EMP) and the hexosemonophosphate pathway (HMP) (EMP/HMP) was calculated on the basis of the 13C population at each carbon in the products. The EMP/ HMP was estimated as 80/20 in glutamic acid fermentation; in contrast, it was 30-40/60-70 in lysine fermentation. These results indicate that HMP contributes much more in lysine fermentation, probably because of the greater requirement of NADPH in lysine formation from glucose.C. glutamicum has been used industrially to produce amino acids by fermentation processes, after Kinoshita et al. (10,11) and Udaka (19) discovered that C. glutamicum could accumulate L-glutamic acid and L-lysine in culture media. Although numerous research reports and reviews (1,15, 21) have appeared concerning fermentation processes and the mechanisms of accumulation of amino acids, attention has been paid mainly to genetic regulation and the enzymological properties of the enzymes involved in amino acids synthesis, and their application to strain improvement. Our interest in amino acids fermentation relates to how the carbons of starting materials (carbohydrates and organic acids etc.) flow through