Lectin-poly(lactide) microsphere conjugates specifically designed for oral administration were prepared and their activity and specificity in presence of mucus were characterized. The presence of hydroxyl or amino groups suitable for covalent coupling of lectins by the glutaraldehyde method at the surface of the microspheres have been ensured by preparing the particles in presence either of poly(vinyl alcohol) (PVA) or bovine serum albumin (BSA). Tomato and asparagus pea lectins could be covalently attached to these particles (1.0-1.3 mg/m(2) of particles). The conjugates demonstrated a 4-10 fold increase in their interactions with mucus compared to control particles. Moreover, the sugar specificity of the lectins was maintained.