Gel delivery vehicles have ideal placement characteristics for periodontal and oral mucosal drug delivery. However, the retention of the vehicle at the site may be of short duration thereby limiting its therapeutic effect. Bioadhesion has received little attention as a means of enhancing vehicle retention in the periodontal pocket and this study aimed to investigate the possible role of this phenomenon to aid oral drug delivery. Chitosan, xanthan gum and poly (ethylene oxide) were selected as potential vehicles from previous in vitro studies, since all 3 had shown good bioadhesive properties. Retention in the periodontal pocket was assessed by means of an insoluble fluorescein marker in 8 patients, and to the oral mucosa by the retention of a small plastic film in 12 subjects. The results showed that fluorescein release from the periodontal pocket was significantly longer for chitosan than for other gels or a water control. In contrast, xanthan gum gave the most prolonged adhesion time on the oral mucosa (153.5 min) followed by poly (ethylene oxide) (89.3 min) and chitosan (42.6 min), and these times were all significantly different from each other (p < 0.05). The results from this study would tend to suggest that the bioadhesive properties of an aqueous gel may be directly related to its retention both in the periodontal pocket and on the oral mucosa. However, other important factors for mucosal adhesion include the patient acceptability of the formulation and the choice of application site.