Twenty-two haematological parameters were measured in 30 patients with systemic lupus erythematosus (SLE) at 110 patient attendances. Using a 10,000 cells per sample automated differential counter, the major abnormalities demonstrated were: lympho-penia, monocytopenia, eosinophilopenia (each of which showed strong correlation with steroid therapy) and increased numbers of cells of high peroxidase activity. Despite the common lymphocytopenia elevation of large unstained cells was noted in 20% of patients. There was no correlation between disease activity and any single laboratory measurement. However, no patient with severe disease had a lymphocyte count above 1.9 × 109/1 or a haemoglobin above 11.7 g/dl