1 Athletes may use benzodiazepines before events to improve sleep, but these drugs may adversely affect performance. 2 Nitrazepam (10 mg) and temazepam (30 mg) were compared with placebo in 27 physical education students, (14 males, 13 females). Treatments were administered at night, using a double-blind, double dummy protocol, for 9 nights. Observations were made in the morning after night 2 and night 9. At least 2 weeks interval was allowed between each treatment. 3 At each examination lung mechanics were measured, a Leeds Sleep Evaluation Questionnaire completed, recognition reaction time, choice reaction time and the critical flicker fusion threshold test were used to assess psychomotor activity and an exercise test was performed. The subject exercised to exhaustion on a bicycle ergometer while ventilation, gas exchange and heart rate were recorded on an FM tape unit for off-line digital analysis. 4 The questionnaire indicated that both drugs were equally effective in promoting and maintaining sleep, but nitrazepam had a marked 'hangover' effect. The psychomotor activity and lung mechanics however seemed unaffected. On day 2, maximum exercise levels attained using either drug were comparable to placebo whilst on day 9 temazepam and placebo were significantly higher than nitrazepam. 5 Heart rate was significantly increased at each exercise level with both drugs. 6 Although there may be some effect of these drugs on athletic performance this is likely to be small especially with temazepam.