Polymer electrolyte membrane fuel cell was supplied with air and a H-2-rich gas obtained by microbial fermentation of molasses from the sugar industry. The energy conversion performance in the fuel cell was examd. under various conditions, including minimum energy input necessary for the prepn. of the gaseous reagents (without pre-cleaning of the fermentation gas, at low airflow, without pressurizing the reagents, and at low fuel cell temp.). The H-2 conversion degree was near 100% but decreased even down to 40% during the fuel cell operation time because of flooding of the anode.