The purpose of this study was to evaluate the effect of a combination of a low dose of chloral hydrate and hydroxyzine on the frontalis muscle electromyogram in addition to other physiologic parameters in pediatric dental patients. A double blind, two-appointment cross-over design was used. Either a placebo or a combination of chloral hydrate and hydroxyzine was given to children during the first visit with the sequence of placebo/ drug conditions being randomly determined. During the second visit, the children received that agent not given during the first visit. Baseline physiologic data was obtained at the beginning of each visit and the physiologic measures were again recorded during topical and local anesthesia administration, high-speed tooth preparation, and at the end of the dental appointment. The results indicated that the frontalis muscle activity and cardiovascular parameters were significantly affected by the drug and dental procedures. Oxygen saturation was least affected. The frontalis muscle appears to be a sensitive physiologic parameter to monitor during conscious sedation as an index of the amount of patient relaxation.