Pediatric oncology/hematology patients, especially those with acute lymphoblastic leukemia (ALL), often undergo repeated painful invasive procedures. Deep sedation, mandatory for these procedures in young children, can reduce patient anxiety and get their compliance during procedures. This study assessed clinical experience of employing methohexital or thiamylal with midazolam as sedative for elective invasive procedures in children with ALL. Between November 1997 and March 2004, 20 out of 33 ALL children received deep sedation after evaluation, mainly because of relatively young age (mean age 4.60 +/- 2.03 years). A total of 176 procedures were done, with 139 being intrathecal therapy. There were 98 and 78 procedures for the methohexital and thiamylal groups, respectively. The average dosages to complete the procedures were 2.2 +/- 1.2 mg/kg for methohexital and 3.4 +/- 2.1 mg/kg for thiamylal. One out of the 176 procedures was failed due to bradycardia, hypotension and cyanosis, in the methohexital group. Otherwise, no significant adverse events were found. Increased heart rate (HR) during stable blood pressure (BP) was observed in both groups. In conclusion, under careful monitoring and performed by experienced practitioners, the application of methohexital or thiamylal combined with midazolam to achieve deep sedation for invasive procedures in young children with ALL is safe.