Five normal volunteers received at a 2-week interval a single dose of sublingual or oral prazepam in double-blind and cross-over conditions. All subjects completed a battery of 15 visual analogue scales before drug intake and 7.5, 15, 22.5, 30, 45, 60, 90 min, 2, 3, 5, 6, 7, 8, 9, 10 and 24 h following intake whereas a computerized assessment of vigilance (reaction time) was performed before intake, 15, 30, 60 min, 2, 3, 6, 8, 10 h following intake. Subjects rated themselves significantly more feeble, clumsy, lethargic, and incompetent following sublingual as compared to oral prazepam while a trend in the same direction was noted for the adjectives muzzy and mentally slow. In contrast, reaction time did not exhibit significantly different changes over time between the two forms. These results suggest a subjectively more rapid onset of activity following sublingual compared to oral prazepam.