Report from the USA.  A 6-year-old male child was scheduled for a dental procedure requiring conscious sedation.  Prior to the procedure, the child was administered a dental cocktail containing chloral hydrate, hydroxyzine and methadone.  After returning from the dentist, the child appeared groggy and was allowed to sleep.  A few hours later, he was found unresponsive, and following resuscitation attempts at a local medical centre, he was pronounced dead.  Toxicological analyses of femoral blood indicated the presence of hydroxyzine at less than 0.54 microg/mL, trichloroethanol (TCE) at 8.3 microg/mL and methadone at 0.51 microg/mL.  No pethidine (meperidine) was detected.  The cause of death was reported to be due to the toxic effects of methadone.  The toxicological analysis was corroborated by the analysis of the contents of the dental cocktail, which revealed the presence of hydroxyzine, chloral hydrate and methadone.  Residue from a control sample obtained from the same pharmacy, but administered to a different subject, was found to contain hydroxyzine, chloral hydrate and pethidine.  This report represents the first known fatality due to accidental substitution of methadone in a dental cocktail.