The interactions of pig gastric mucin and bovine submaxillary mucin with carboxylate (PCM) and amino (PAM) polystyrene latexes with 750 and 1000 nm diameters have been studied in vitro. The mucin interaction increased when the pH decreased from 7.4 to 3.0 and when the electrolyte concentration increased from 86 to 205 mM. The driving force of the interaction was very probably nonionic. Under certain conditions, electrostatic attraction also was important for PAM. Under all experimental conditions tested, the mucins interacted less with PAM than with PCM. The functional groups of the latexes directed the conformation of the adsorbed mucins at the interface. At low pH, the mucins probably were adsorbed in multilayers.