Previous attempts to evaluate the transport of proteins across the intestinal mucosa using the caco-2 cell line have neglected the mucus layer as a barrier to drug absorption. To achieve a more accurate assessment of the absorption a coculture can be used that combines the enterocyte-like transport properties of the caco-2 cell line with the gastric mucin secretion of the HT29-MTX cell line. Understanding the degree to which micro- and nanoparticulate poly(methacrylic acid-g-ethylene glycol) (P(MAA-g-EG)) drug carriers may act as paracellular permeation enhancers may also require the presence of the mucus barrier. In this study we utilize quantitative fluorescence microscopy and transepithelial resistance to analyze the effect of drug carrier size on the tight junction integrity. In this study Caco-2 and HT29-MTX monolayers were grown on polycarbonate Costar® transwell membranes for 21 days until confluent. Monolayers were exposed to P(MAA-g-EG) microparticles or nanoparticles in the apical chamber. Methanol fixed memebranes were immunolabeled for E-cadherin and ZO-1 and imaged using laser scanning confocal microscopy. The mucus secretion of the monolayers was confirmed by transmission electron microscopy and alcian blue staining. Of the junctional complex molecules chosen, E-cadherin appears to be the most advantageous as a marker for the integrity of the epithelial. Besides for providing the strongest signal, the calcium dependent of binding of E-cadherins has been shown to be coupled with the disruption of both claudin1 and ZO-1. The inhomogeneous staining of claudin-1 suggests that expression is different between the Caco-2 and HT29-MTX cell lines.