ABSTRACT: BACKGROUND: A routine method for the quantification of beryllium in biological fluids is essential for the development of a chelation therapy for Chronic Beryllium Disease (CBD). We describe a procedure for the direct determination of beryllium in undigested micro quantities of human blood and serum using graphite furnace atomic absorption spectrometry. Blood and serum samples are prepared respectively by a simple 8-fold and 5-fold dilution with a Nash Reagent. Three experimental setups are compared: using no modifier, using magnesium nitrate and using palladium/citric acid as chemical modifiers. RESULTS: In serum, both modifiers did not improve the method sensitivity, the optimal pyrolysis and atomization temperatures are 1000 degrees C and 2900 degrees C, respectively. In blood, 6 mug of magnesium nitrate was found to improve the method sensitivity. The optimal pyrolysis and atomization temperatures were 800 degrees C and 2800 degrees C respectively. CONCLUSION: In serum, the method detection limit was 2 ng l-1, the characteristic mass was 0.22 (+/- 0.07) pg and the accuracy ranged from 95 to 100%. In blood, the detection limit was 7 ng l-1, the characteristic mass was 0.20 (+/- 0.02) pg and the accuracy ranged from 99 to 101%.