In order to measure caries inhibition by means of the local application of fluoride gel and a new fluoride-containing varnish, three groups of Osborne-Mendel rats, each consisting of 20 animals, were tested in a short-term experiment. Amine fluoride containing gel and fluoride varnish were applied with a soft paint brush to the molars of each half-mandible. The diet Stephan 580 and distilled water were given ad libitum 2 h after the application of the fluoride preparation. By comparing the severity of the lesions produced, both fluoride-containing agents were shown to exhibit caries-inhibiting activity. The gel which contained the amine fluoride, and the fluoride-containing varnish, showed a fairly similar degree of inhibition when compared to the control group.