The adherence of microorganisms to contact lenses may be an important initial step in the pathogenesis of contact lens-associated infectious keratitis. Using a strain of Candida albicans whose interaction with various polymers has been well characterized we systematically investigated the adherence of this pathogen to hard hydrophobic and soft hydrophilic extended-wear contact lenses. Yeasts adhere to the hydrophobic lenses in direct proportion to the wetting angle of the lens whereas yeasts adhere to the hydrophilic lenses in direct proportion to the water content of the lens. Tear proteins such as albumin, lactoferrin, and lysozyme in addition to fibronectin enhance yeast adherence to both types of lenses (P<0.01). Concanavalin A reduces adherence of yeasts to both lens types (P<0.01). Among tear components however, only mucin (0.5%) consistently reduced yeast adherence to both lens types. Hydrophilic extended wear lenses worn for at least 28 days by normal patients consistently had greater adherence of yeasts than unworn lenses of the same type, often as much as ten-fold or greater yeasts/mm2of lens surface area (P<0.05). These investigations indicate that tear components both in solution and adsorbed to the lens surface enhance microorganism adherence to contact lenses.