Abstract: A solution of BH4- in aqueous 1% NaOH was injected into a carrier stream (2 ml/min) of water, which was mixed with a stream (2 ml/min) of 25 mM As(III) in 1 M HCl in a mixing coil (30 cm x 0.5 mm). The AsH3 formed diffused through the PTFE membrane of a gas diffusion unit into an acceptor solution (0.01 M H2SO4) and the resulting solution passed through the thin-layer flow cell of a BAS LC-17A amperometric detector equipped with dual Pt working electrodes maintained at 0.8 V vs. Ag/AgCl. The calibration graph was linear from 8 µM to 1 mM BH4-, and the detection limit was 1 µM. The RSD at 60 µM was 2% and the sample throughput was 60/h. Serious interference was caused by sulfide and sulfite.