Head column-field amplified sample stacking (HC-FASS) is one of the most powerful concentration techniques in capillary electrophoresis. In the present work we demonstrate that a laboratory-designed pneumatic sampler not only enables us to easily perform HC-FASS from stagnant sample solutions but also permits us to carry out HC-FASS from sample stream, which creates an opportunity to lower the detection limit of analytes further. The influence of stacking time in case of the flowing sample on peak efficiencies and resolution is discussed. It is demonstrated that the sample plug length can be kept constant by monitoring the current in the capillary, which controls a feedback system based on backpressure at the capillary outlet.