A withdrawal syndrome occurred in two patients after substitution of a short-acting benzodiazepine for a long-acting benzodiazepine. Both patients had used long-acting benzodiazepines on a daily basis for many years. In one case, oxazepam was substituted for diazepam, and in the other, temazepam was substituted for flurazepam hydrochloride. In both cases the short-acting benzodiazepine was substituted in a once-daily dosage. Withdrawal symptoms followed and persisted for at least one month. Relative advantages and disadvantages of short-acting and long-acting benzodiazepines are discussed.