Retrospective comparison of peripheral haematological values in normal volunteers and patients on anti-epileptic drugs over a one year period demonstrated a significant reduction in total white blood cells, neutrophil, eosinophil, lymphocyte and monocyte counts in patients. The red blood cell count, mean cell volume and mean cell haemoglobin were significantly reduced in the patients. These findings need to be taken into account when new anti-epileptic drugs are assessed by adding on to existing therapy.