Residual and acute effects of flurazepam and triazolam were studied in two double-blind, crossover, placebo controlled, single-dose experiments. Psychological and physiological effects were determined 10 h after night administration (flurazepam 30 mg and triazolam 0.5 mg), and for 6 h after morning ingestion (flurazepam 15 mg and triazolam 0.25 mg). Both drugs produced similar "hangover" effects, impairing motor performance and increasing sleepiness on the following morning. After morning administration pronounced sedative effects were found with triazolam, while flurazepam effects were mild and hard to distinguish from placebo. The clinical relevance of these findings is discussed, suggesting that these drugs may be conceived as belonging to two different types of hypnotic agents.