A new potentiometric gas sensing concept is used in conjunction with a flow injection technique to rapidly determine ammonia-nitrogen in the 10−5to 10−2mol/L range. The system designed utilizes a novel tubular flow-through PVC-nonactin membrane electrode to detect ammonium ions formed in a recipient buffer stream as the sample flows through a gas dialysis unit. At least 30 samples/h can be determined with good precision (⩽ ± 7%) for samples ⩾ 10−5mol/L in ammonia-N. Preliminary data concerning the analytical application of this system for blood ammonia-N measurements is presented. A novel gas dialysis method for removing ammonia from blood samples is also described.