We evaluated the safety and efficacy of midazolam-ketamine association to control pain induced by diagnostic procedures in paediatric oncology patients. 226 procedures were carried out in 92 patients aged three days to 18 years. Drugs were given i.v. by an anaesthesiologist. Midazolam dose was 25 microg.kg-1 and ketamine 0. 5 to 2 mg.kg-1, depending on number and invasiveness of procedures. The mean dose of ketamine was 1 mg.kg-1. Mean duration of sedation was ten min. No complication was observed and analgesia was considered satisfactory in 89 out of 92 patients. These results indicate that midazolam-ketamine is a safe and effective association in pain management for paediatric oncology patients and efficiently induces brief unconscious sedation with analgesia.