The levels of 1,3‐propanediol dehydrogenase and of the glycerol dehydrogenase in Clostridium butyricum grown on glucose–glycerol mixtures were similar to those found in extracts of cells grown on glycerol alone, which can explain the simultaneous glucose–glycerol consumption. On glycerol, 43% of glycerol was oxidized to organic acids to obtain energy for growth and 57% to produce 1,3‐propanediol. With glucose–glycerol mixtures, glucose catabolism was used by the cells to produce energy through the acetate–butyrate production and NADH, whereas glycerol was used chiefly in the utilization of the reducing power since 92–93% of the glycerol flow was converted through the 1,3‐propanediol pathway. The apparent Kms for the glycerol dehydrogenase was 16‐fold higher for the glycerol than that for the glyceraldehyde in the case of the glyceraldehyde‐3‐phosphate dehydrogenase and fourfold higher for the NAD+, providing an explanation for the shift of the glycerol flow toward 1,3‐propanediol when cells were grown on glucose–glycerol mixtures.