The authors have studied the pharmacokinetics of the five benzodiazepines: flurazepam, flunitrazepam, nitrazepam, temazepam and triazolam. The pharmacokinetics parameters of these molecules are different and vary according to individual sensitivity. Twelve healthy volunteers were involved in this study (6 males--6 females). The parent drug has been titrated for nitrazepam, flunitrazepam, temazepam, triazolam and the active metabolite of flurazepam, the N-desakylflurazepam (DAF). Half-lifes have been calculated: it is short for the temazepam and triazolam with no accumulation after multiple drug administration. Triazolam has the shortest half-life. Those different results enable to better understand the prescription problem of hypnotics as duration of action must be limited to one night, with no residual effect the day after.