The VGA-76 Operation Manual recommends the use of Digestion Procedures sodium borohydride as the reducing agent in the determination of mercury, the solution containing 0.3% NaBH4 in 0.5% NaOH. It has been found in the present study that while sodium borohydride provides a slightly more sensitive response than stannous chloride (25% SnCl2 w/v in 20% v/v HCI) for nitric acid standard solutions, a severe interference exists in the analysis of fish sample digests.