Product formation during anaerobic degradation of glycerol by Klebsiella pneumoniae DSM 2026, under glycerol limitation and glycerol excess in continuous cultures, has been investigated. Major and minor products and by-products as well as gaseous products were measured. The results indicated a positive correlation between specific glycerol uptake and most product formation rates under glycerol limitation. The production of 1,3-propanediol, lactate, formate, acetate, succinate and the by-products of anaerobic glycerol degradation by K. pneumoniae, acetoin and 2,3-butanediol, was favoured by glycerol excess, while hydrogen generation and ethanol formation were best under glycerol limitation. It was also found that under glycerol limitation the rate of hydrogen evolution was generally higher than the CO2 production rate while under excess glycerol the reverse was true. Hence, on the basis of the ratio of the specific rates of evolution of H-2 and CO2 (q(H2)/q(CO2)), it is possible to infer the existence of glycerol limitation. On the basis of the carbon and available electron balances, which are independent of metabolic pathways, the data are consistent. The NADH, balance, which took into consideration the pathways of product formation, was also tested to check the validity of the assumed pathways and to check critically the consistency of the data. Good balances were also obtained.