Polymorphonuclear leukocytes (PMN) from patients with systemic lupus erythematosus (SLE) produced fewer reactive oxygen species (ROS) than PMN from healthy blood donors. The capacities of PMN from healthy blood donors (HBD), n = 38, and SLE patients, n = 92, to produce ROS upon activation with phorbol 12-myristate 13-acetate or opsonised E. coli were investigated using flow cytometry. The amount of ROS produced is shown as geometric mean fluorescence intensity (geo mean fluorescence, MFI). The two-sided Mann-Whitney test was used to calculate the level of significance. The horizontal lines represent the median value of each dataset.