Controlled delivery of diagnostic or therapeutically active agents to the eye and oral cavity is limited by the efficient removal mechanisms that exist in these areas. In this work, recently isolated, purified and characterised Brazilian bean lectins were examined for their ability to bind to the buccal and sublingual mucosa, cornea and conjunctiva of rat, with regard to their potential therapeutic use. These lectins were labelled using biotin (long arm) N-hydroxysuccinimide ester and a technique developed at the University of Portsmouth. Evaluation of binding after 15 min contact with intact (unfixed) rat eye and oral cavity epithelia was completed using a standard histological procedure involving the avidin-biotin reaction and formation of a brown precipitate with a 3,3'-diaminobenzidine solution. When examined by affinity chromatography, all lectins studied were found to show high percentage biotinylation (i.e. less than 4% by weight of total lectin was eluted from the column). The lectin:biotin ratio was estimated using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), and ranged between 1:2 (Cratylia floribunda) and 1:10.4 (Canavalia brasilensis). As with previous studies, all lectins bound to the mucosal surfaces to some extent--the Cratylia floribunda lectin appearing to be the most promising, whereas the Dioclea violacea lectin showed comparatively weak binding. In all cases, the presence of glucose (the hapten sugar) reduced or eliminated binding. It was concluded that glucose-mannose binding sites are present on these surfaces, and the lectins from C. floribunda showed a particular affinity for these.