Glutamate dehydrogenase is immobilized on poly(vinyl alcohol) beads and packed into a stainless-steel column (3 cm X 4 mm i.d.). Serum is deproteinized with tungstic acid. Sample solution (30-mu-l) is injected into the carrier stream [5 mM NAD+ in glycine buffer (pH 9.5)]. The NADH formed is detected at 465 nm (excitation at 340 nm). The calibration graph is linear for 0.5 - 500-mu-M glutamate; the detection limit is 0.2-mu-M.