Direct force measurements were used to investigate the interactions between grafted poly(ethylene glycol) (PEG) (M-W 2000) and both adsorbed and soluble bovine submaxillary gland mucin. These measurements show that both soluble and adsorbed mucin adhere weakly to the grafted PEG layers. Soluble mucin mediates a concentration-dependent, bridging attraction between the PEG films. Similarly, PEG adheres to adsorbed mucin layers in both the presence and absence of 0.2 mg/mL mucin solutions. The heteropolymer attraction is pH dependent, with the adhesion being substantially higher at pH 2 than at pH 7.2. The latter suggests that hydrogen-bonding interactions are responsible for binding. The weaker mucin interactions at pH 7.2, however, allow for PEG-coated surfaces to adhere to surface-bound mucin in the presence of soluble mucin. Such characteristics are particularly desirable for coatings for oral drug carriers.