The present invention relates to use of a milk apoprotein or a mixture thereof to prevent or treat microbial or viral infection of the human or animal body. It is believed that this is achieved by inhibiting adhesion of potential pathogens. More preferably, at least one milk apoprotein or a mixture thereof is administered, simultaneously or sequentially, with either or both of at least one free fatty acid or a mixture thereof or a monoglyceride thereof; and/or at least one organic acid or a salt or ester thereof or a mixture thereof. The active agent(s) may be delivered by means of a pharmaceutically acceptable delivery system which includes parenteral solutions, ointments, eye drops, nasal sprays, intravaginal devices, surgical dressings, medical foods or drinks, oral healthcare formulations and medicaments for mucosal applications.