In a double-blind, placebo-controlled sleep-laboratory study the short-term effects of cinolazepam--a recently introduced 1,4 benzodiazepine with a half-life of 9 h--on the all-night sleep, morning awakening and early morning behaviour were investigated in 20 young normal subjects, whose sleep was experimentally disturbed by nocturnal traffic noise. The latter was prerecorded on tape and reproduced by loud speakers throughout the night with a sound pressure level of 68-90 dB(A) (energy equivalent mean noise level LAeq: 79dB(A)). According to the parallel group design subjects received either a placebo or 40 mg cinolazepam. Specifically, they spent nine nights in the sleep laboratory: two adaptation nights, one baseline night on placebo, three drug or placebo nights, and three post-drug/placebo nights under traffic noise. Somnopolygraphic investigations were carried out between 22h30 and 06h00. The drug was given orally half an hour before bedtime. Each 30 sec epoch was scored according to the criteria of Rechtschaffen and Kales. In the morning the subjects were awakened by 1000 Hz tones which were increased in loudness in 10 dB steps in two minute intervals. A sleep self-rating scale for sleep and awakening quality was completed half an hour after the morning toilet. Thereafter noopsychic and thymopsychic variables were evaluated utilizing a psychometric test battery. Statistical analyses of objective sleep variables demonstrated a significant improvement of sleep maintenance after 40 mg cinolazepam as reflected by an increase of sleep efficiency, decrease of wake time (during total sleep period) and number of awakenings as compared with the placebo. Sleep architecture was only affected slightly: sleep stage S1 decreased, S2 increased, while S3, S4 and SREM (S rapid eye movement) remained unchanged. Subjective sleep quality improved significantly as well. In the mornings there were no hangover signs, neither in subjective nor in objective psychometric and psychophysiological variables. Finally, the study suggests that man can adapt subjectively to nocturnal traffic noise over one week, although the improvement of objective sleep variables over time did not reach the level of statistical significance.