Triazolam (U-33030), an investigational hypnotic drug, was evaluated in seven insomniac subjects in the sleep laboratory. The protocol consisted of 22 consecutive nights: four placebo nights for adaptation and baseline, two weeks of drug administration (0.5 mg triazolam) for short- and intermediate-term drug effectiveness, and four placebo nights for withdrawal effects. With short-term drug use, both sleep induction and sleep maintenance improved, with total wake time decreasing markedly--a 45 per cent decrease from baseline. At the end of two weeks of drug use, none of the efficacy parameters was significantly decreased from baseline; there was only a 17 per cent decrease in total wake time. Following drug withdrawal, sleep difficulty significantly increased above baseline levels. Two of the subjects experienced episodes of amnesia during the drug administration period. The per cent of REM sleep decreased significantly during both short and intermediate drug conditions. Following drug withdrawal, the per cent of REM sleep was similar to baseline. Slow-wave (stages 3 and 4) sleep was significantly decreased for both drug conditions; and following drug withdrawal, it returned completely to the baseline leve. These data indicate that triazolam is effective for short-term use, loses most of its effectiveness with intermediate-term use, and its withdrawal is followed by a significant sorsening of sleep. These findings are discussed in relation to the potential labeling and promotion of triazolam. Finally, the findings of amnesia associated with triazolam administration need to be more thoroughly evaluated.