1. In a double-blind cross-over study 8 athletes received during 2 sessions of 2 nights zopiclone (7.5 mg) or placebo. 2. Residual effects on subsequent daytime functions were evaluated both subjectively by visual analogue scales as well as objectively by a test battery measuring psychomotor and physical skills. 3. Zopiclone had some favourable effects on self-estimated sleep quality and daytime sleepiness. 4. Psychomotor and physical performance tests did not show any significant difference between zopiclone and placebo. 5. We conclude that zopiclone has useful hypnotic activity without significant adverse effects on athletic performance.