A method for producing an oligomeric form of .alpha.-lactalbumin which is in the molten globule-like state is described. The method suitably comprises exposing a source of .alpha.-lactalbumin in which the .alpha.-lactalbumin is preferably in the molten globule-like state, to an ion exchange medium which has been pre-treated with casein or an active component thereof, such as oleic acid, and recovering .alpha.-lactalbumin in an oligomeric form therefrom. Pre-treatment of the ion exchange medium, particularly with casein derived from human milk, has been found to significantly improve yields of the oligomeric form of .alpha.-lactalbumin and means that it can be readily isolated from readily available sources such as bovine .alpha.-lactalbumin. This form of .alpha.-lactalbumin is useful therapeutically, in particular as an antibacterial agent and also as an anti-cancer therapeutic.