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Technique for the performance of the nitro-blue tetrazolium (NBT) test. Blood is obtained in glass tubes, using heparin as anticoagulant (the concentration of heparin should be 75-100 units/ml of blood). The usual amounts of blood required from the patient is never more than 10 ml. Pipette 0 1 ml of the blood into a well of the plastic tray. Make the 'working' NBT solution by mixing equal volumes of the stock 0.2 % solution and the phosphate-buffered saline. This solution must be made freshly for each batch of tests. Pipette 0.1 ml of the 'working' NBT solution into each well containing blood and mix the contents. Cover the tray with another tray to ensure humidity, and incubate at 37°C for 15 minutes. Follow this with an equal period at room temperature. Using a Pasteur pipette, or a large bacteriological loop, with which to transfer the blood-NBT mixture, make careful coverslip smears and allow them to dry in air. Fix the smears in methanol for three minutes. Stain with Pappenheim's stain for three to five minutes. (The actual time is best decided by trial, the desired result being to stain the granulocyte nuclei green and to leave most of the erythrocytes as 'ghosts'). Air dry and mount in DePeX. Examine under the 40 x objective and assess the number of neutrophils containing the formazan deposit as a percentage.