1,3-Propanediol production by Klebsiella pneumoniae was studied in batch cultures under N-2 flow and four airflow systems. Different byproducts were formed under different aeration conditions. An anaerobic/aerobic combined fed-batch culture was developed giving 70 g 1,3-propanediol 1(-1) and 16 g 2,3-butanediol 1(-1) with total diol yield of 0.6 mol(-1) glycerol.