This study determined the dose effects of zolpidem in 12 healthy males with normal sleep patterns. Subjects spent 7 weeks, 3 consecutive nights per week, in the laboratory and had a 4-night washout between treatments. The first week was a screening and adaptation week. Then subjects received zolpidem (2.5, 5.0, 7.5, 10.0, or 20.0 mg) or placebo on the first two nights for each of the next 6 consecutive weeks. Treatments were organized in a Latin square design and administered in a double-blind fashion. On the third night of each treatment, subjects always received placebo. The 5.0 mg and larger doses of zolpidem significantly decreased latency to persistent sleep and wake before sleep. Sleep maintenance measures were not affected by zolpidem. The 7.5 mg and higher doses of zolpidem significantly increased total sleep time. The only significant sleep stage effect was a decrease in percent of rapid eye movement sleep at only the 20 mg dose. No consistent discontinuation effects were found. Zolpidem was hypnotically active at doses as low as 5.0 and 7.5 mg, and sleep stage effects occurred only at the 20 mg dose, thus separating the dose range of hypnotic and sleep stage effects.