A membrane filtration procedure for the preconcentration and separation of Pb(II) at trace levels has been established. Cellulose nitrate membrane filters were used. The procedure is based on chelate formation of Pb(II) with Brillant Black BN and on the adsorption of the chelates on a cellulose nitrate membrane filter. The cellulose nitrate membrane was completely dissolved in 0.5 mL nitric acid and completed to 5 mL with water. Lead determinations were performed by flame atomic absorption spectrometry. Lead was quantitatively recovered at pH 7.0 with 0.75 mg of Brillant Black BN at 4 mL mint flow rate. The detection limit for lead and the preconcentration factor were 1.5 mu g/L and 50, respectively. Validation of the method was checked by using certified reference materials SPS-WW2 Wastewater Level 2 and GBW 07424 Soil. The method was applied to natural water samples for the determination of lead with satisfactory results.