Reactive oxygen species (ROS) production in polymorphonuclear leukocytes (PMN) from systemic lupus erythematosus (SLE) patients did not correlate with Hydroxychloroquine treatment or the dose of prednisone. ROS production was measured by flow cytometry after ex vivo activation of PMN with phorbol 12-myristate 13-acetate (A) the amount ROS produced by SLE-PMN, treated with or without Hydroxychloroquine. (B) The amount of ROS produced in individual patients plotted against the dose of prednisone at the day of sampling. The amount ROS produced is shown as geometric mean fluorescence intensity (geo mean fluorescence, MFI). The line represents the median value of each dataset.