To control benzodiazepine abuse in Hong Kong, the Government's Pharmacy and Poisons Board reclassified benzodiazepines as Dangerous Drugs in October 1990. Apart from formal prescriptions, detailed records were then required for the supply and dispensing of these drugs. These regulations were applied initially only to brotizolam, triazolam and flunitrazepam, and were extended in January 1992 to include all benzodiazepines. The impact of these regulatory changes on benzodiazepine use has been studied by analyzing the sales patterns of seven benzodiazepines between 1990-1993. In 1991, the sales of flunitrazepam and triazolam fell, but the sales of five unrestricted benzodiazepines increased. In 1992-1993, the sales of all but one of the benzodiazepines fell. Comparing 1993 to 1990, the fall in sales was particularly marked for triazolam, chlordiazepoxide and flunitrazepam. A regulation requiring the use of proper prescriptions and detailed records for the supply and dispensing of benzodiazepines, appears to have curbed, at least partially, their abuse in Hong Kong.