The effects of oral loprazolam (1, 2 mg) on vigilance, attention, immediate memory, short-term memory, learning, long-term non-consolidated and long-term consolidated memory were determined. Twelve healthy young male volunteers were given all the treatments, placebo or loprazolam, on three different occasions, in a double-blind, random latin-square sequence, crossing over every 2 weeks. Volunteers completed a battery of tests at night, 3.5 h after drug administration, and in the morning, 10 h after drug administration, to test recall of some of the material presented at night (long-term memory) and residual effects. Loprazolam did not significantly impair any of the functions tested at night. On the other hand, 2 mg loprazolam caused impairment of long-term memory, both consolidated and not. This reduction of long-term memory does not seem to be related to the impairments of vigilance, attention or learning. The 2 mg dose of loprazolam, which did not modify the mean scores and improved vigilance, attention and learning in some of the subjects, reduced long-term memory. Therefore, although caution in interpreting the results should be used, mainly because it is possible that differences in sensitivity of the tests cannot be overcome and because the relative small number of subjects, our results indicate that loprazolam might induce selective impairment of long-term memory. Since there were no differences between the effects on consolidated and non-consolidated memory, the amnesic effect of loprazolam seems to be due to a decrease in the storage of memory traces. There were no clear generalized residual effects in the morning after administration.