Oral transmucosal fentanyl citrate (OTFC) is a novel, noninvasive dosage form of fentanyl used to provide children and adults with sedation, anxiolysis, and analgesia. In order to determine the bioavailability and absorption of fentanyl from OTFC, 12 volunteers were given intravenous fentanyl citrate or OTFC 15 μg/kg on each of two occasions. On a third occasion, the authors assessed oral administration (gastrointestinal absorption) by giving eight of the same volunteers the same dose of a solution of fentanyl citrate to swallow. In each study, arterial blood samples were taken over 24 h for analysis of plasma fentanyl. After intravenous (iv) administration of fentanyl, clearance (mean ± standard deviation) was 0.67 ± 0.15 1/min; volume of distribution at steady state was 287 ± 79 1; and the terminal elimination half-life was 425 ± 102 min. Peak plasma concentrations of fentanyl were higher (3.0 ± 1.0 vs. 1.6 ± 0.6 μg/ml, P = 0.01) and occurred sooner (22 ± 2.5 vs. 101 ± 48.8 min, P = 0.003) after OTFC than after oral solution administration. Plasma concentrations of fentanyl after OTFC decreased rapidly, to less than 1.0 ng/ml within 75–135 min after the beginning of administration. Peak absorption rate was greater (11.1 ± 4.3 vs. 3.6 ± 2.1 μg/min, P = 0.004) and occurred much sooner after OTFC than after oral solution administration (19 ± 2.6 vs. 87.5 ± 38.1 min, P = 0.001). Systemic bioavailability was greater after OTFC administration than after the oral solution (0.52 ± 0.1 vs. 0.32 ± 0.1, P = 0.01). Terminal elimination half-life was similar after all modes of fentanyl delivery–OTFC (460 ± 313 min), iv (425 ± 102 min), or oral solution (469 ± 123 min). These results suggest that although absorption of fentanyl from OTFC occurs through both the oral mucosa and the gastrointestinal tract, it is more rapid at the former. The data also indicate that sequestration of fentanyl in the oral mucosa is minimal.