Recurrent aphthous ulcers of the mouth are difficult to treat because of no known definite aetiology. This paper presents the use of lactic acid bacteria thought to modulate the host immune response to affect improvements in the disease. Twenty-five patients with the disease were treated with 6 lactic bacteria capsules (in the form of OMX capsules) daily for a period of six months, and their responses were evaluated. Seventeen patients (73.9%) became free of the disease six months later, while 6 (26.1 %) experienced very dramatic improvements. Two patients were lost to follow-up. It is concluded that lactic acid bacteria is beneficial in the treatment of recurrent aphthous ulcers of the mouth.