No / Improving the patient¿s experience of a bone marrow biopsy ¿ an RCT Aims. To compare nitrous oxide 50%/oxygen 50% (N2O/O2 ¿ entonox) plus local anaesthetic (LA) with placebo (oxygen) plus LA in the management of pain experienced by patients undergoing a bone marrow biopsy. . Bone marrow biopsies are a common procedure for many haematological conditions. Despite the use of a LA, pain during the procedure has frequently been reported by patients. Previous research in pain management of other invasive diagnostic procedures (e.g. sigmoidoscopy) has reported N2O/O2 as an effective alternative to LA. Design. Double-blind randomized controlled trial. Methods. Forty-eight patients requiring a bone marrow biopsy were randomized to receive either N2O/O2 or oxygen in addition to their LA. Participants were asked to complete a pain score and comment on their experience of the procedure. Results. Although the overall pain scores were moderate, there was a wide range of scores. N2O/O2 resulted in significantly less pain for men, but not for women. All patients who had had previous biopsies reported significantly more pain, regardless of the gas used. There were no significant adverse effects in either group. Conclusion. N2O/O2 is a safe, effective, easy-to-use analgesic which merits further investigation in potentially painful diagnostic (and other) interventions.