For many drugs, buccal route offers many advantages over conventional routes of delivery with an improved bioavailability due to the avoidance of degradation in the gastrointestinal tract and hepatic first-pass metabolism. However, the major limitation to buccal drug delivery is the permeability barrier in the buccal mucosa. Use of penetration enhancers appears to be a pertinent approach to increase the drug permeation through the buccal epithelium. Buccal bioadhesive tablet formulations enable a delivery with a plasma drug level of the desired therapeutic response for a defined period of time, and also provides a means of confining the drug and penetration enhancer to a defined region of the mucosa. In this study, a bioadhesive tablet formulation for buccal delivery was designed using a mixture of hydroxypropyl methylcellulose and carbomer, incorporated with a penetration enhancer, sodium glycodeoxycholate (GDC). In vitro bioadhesion property of the formulated tablet was examined and histological study was carried out to examine an in vivo interaction between the tablet and tissue. GDC did not affect the adhesiveness of the tablet which makes it an acceptable excipient for a buccal bioadhesive drug delivery system. Histological changes such as loss of upper cell layers and formation of vacuoles as well swelling in the cells were observed in the buccal epithelium, after 4 h contact with the tablets containing GDC. Studies on reversibility of the interaction are in progress. (C) 1998 Elsevier Science B.V. All rights reserved.