With a cell concentration of 125 g dry biomass 1(-1) and a dilution rate of 0.1 h -1, Propionibacterium acidipropionici produces 30 g propionic acid 1(-1) from sugar with a productivity of 3 g1(-1) h (-1). The yield of propionic acid is approx. 0.36-0.45 g propionic acid g-l sucrose and is independent of the dilution rate and cell concentration. Acetic acid is an unwanted by-product in the production of propionic acid. The concentration of acetic acid only increases slightly when the cell concentration is increased. A two-stage fermentation process was developed for the conversion of sugar or molasses of various types to propionic acid and vitamin B-12. By fermentation of blackstrap molasses (from sugar beet and sugar cane) in the first fermentation stage 17.7 g propionic acid 1(-1) with a yield of 0.5 g propionic acid g(-1) carbohydrate was produced with a dilution rate of 0.25 h(-1). In the second stage 49 mg vitamin B-12 1(-1) was produced at a dilution rate of 0.03 h(-1).