This study was undertaken to determine the dosages, treatment times and side effects of ketamine HCI with and without two benzodiazepines when used for sedation on a group of precooperative children at the UCLA Children's Dental Center. Ketamine was evaluated when used alone, and in conjunction with two benzodiazepines, diazepam or a new water-soluble midazolam. An anti-muscarinic, atropine or glycopyrrolate, and nitrous oxide-oxygen were included in all sedations. Mean treatment times were increased significantly when ketamine and a benzodiazepine were used in combination. Additionally, mean ketamine dosages were decreased significantly when ketamine was utilized in combination with a benzodiazepine. All children tolerated the sedation well and there were no severe adverse reactions. Side effects included nausea, vomiting, and a rise in post-operative temperatures.