A procedure is described and evaluated for isolating leucocytes from 15 ml of whole blood using a modified dextran sedimentation procedure. The mean recovery of leucocytes is 62% without differential white cell loss, and there is no contamination from red cells, platelets or plasma. Digestion of leucocytes with nitric acid is performed prior to the determination by atomic-absorption spectrophotometry of zinc using flame atomisation and of copper by electrothermal atomisation. The relative standard deviations for the determinations range between 2.2 and 3.6%. The range reported for zinc in leucocytes is 68–246 pmol per 106 cells and 4.1–36.8 per 106 cells for copper. These results are compared with those from other studies.