Patients in whom a bone marrow biopsy is planned will be randomised to one of two groups - a control-TENS group where the TENS machine will be set at the lowest sensory threshold and an intervention-TENS group where the TENS machine will be set at a recognised analgesic level (>50 Hertz (Hz) and below the pain threshold for the patient) (Bennett et al. 2011). The identity of the TENS type will be concealed from both the patient and the doctor performing the biopsy. The primary outcome will be pain and this will be recorded by the patient immediately after the procedure using a validated numerical scale (0-10). All patients will receive standard pain relief (ie. local anaesthetic with or without inhaled nitrous oxide).