Technical Abstract: A peer-verified, solid-phase extraction/anion exchange LC method for determination of niacin in milk-based and soy-based infant formula is presented. Sample digestion utilizes a standard AOAC digestion procedure that involves autoclaving 121 degree C for 45 min in (1+1) h2so4 to free endogenous niacin from protein and to convert added niacinamide to niacin. Adjusting the digest solution to pH 6.5 with 7.5 N NaOH and acidification to pH <1.0 with (1+1) H2SO4 precipitates protein. Solid-phase extraction (spe) of niacin is accomplished by passing an aliquot of the digest solution over an Aromatic Sulfonic Acid-spe (ArSCX-spc) column. After washing the column with methanol and demineralized water to remove extraneous materials, the niacin is eluted using 0.25 M NaAc/HOAc buffer at pH=5.6. LC separation is accomplished using an anion-exchange polystyrene-divinylbenzene column with a 0.1 M NaAc/HOAc buffer at pH=4.0. Niacin is deleted by UV detection at 260-nm wavelength. A standard curve is prepared by passing known amounts of niacin over the ArSCX-spc columns used for niacin extraction. The following mean and rsd values were obtained for the NISR SRM 1846-Infant Formula with a certified value for niacin of 63.3 +/-7.6 ug/g. Submitting laboratory: 59.7 +/-7.6 ug/g => 6.7 % rsd, n = 27. Collaborating laboratory: 56.6 +/- 6.6 ug/g =>11.7 % rsd; n = 10.