Bone marrow aspiration and biopsy is a procedure of central importance in the diagnosis of haematological disease and is one that can be safely performed in the outpatient clinic using only local anaesthesia. We evaluated the role of inhaled nitrous oxide (Entonox) as an adjuvant to local anaesthesia (LA) in patients requiring bone examination. We prospectively studied the role of Entonox in patients attending our outpatient department who required bone marrow examination. All patients received LA with injected 2% lignocaine but patients were then assigned to either LA alone or LA plus inhaled Entonox. Following the procedure patients were given a questionnaire and asked to score the discomfort associated with the procedure. Twenty-eight of 85 patients (33%) who received LA alone scored their pain as 3 (severe) compared with seven of 51 patients (14%) who received LA plus Entonox, P = 0.013. No adverse events were associated with Entonox use. Forty-three of the 51 patients who received Entonox stated that they would prefer to use this method of anaesthesia again. We conclude that inhaled Entonox is a useful adjuvant to local anaesthesia for patients undergoing bone marrow examination.