The extent of bioavailability of midazolam following sublingual and oral administration were evaluated. Three healthy volunteers received a single 15-mg dose of midazolam maleate by sublingual and oral routes on two occasions in a ossover design. Concentrations of midazolam in plasma during 4 h after each dose were measured by gas-liquid chromatography with an electron-capture detector. The mean AUC0-4 value following sublingual administration was significantly greater than that following oral administration (14889 vs 3594 ng. min/ml, p less than 0.05). The peak plasma concentration after sublingual dose was also significantly higher than that after oral administration (p less than 0.05). The mean AUC0-4 value of midazolam after sublingual administration was increased four times compared with that after oral administration, possibly due to avoidance of first-pass effect. Thus, the clinical effects of midazolam may likewise be enhanced by sublingual administration of midazolam.