The effect on local plaque formation of a varnish containing 1% chlorhexidine and 1% thymol (Cervitec) was evaluated. Ten volunteers with clinically healthy oral conditions were asked to refrain from any kind of oral hygiene measures for three periods of three days. Undisturbed plaque formation was recorded during the first experimental period. At the beginning of the second period, the varnish was applied to six vestibular enamel surfaces and removed after 1 h. The third experimental period was initiated 12 weeks after varnish application to assess a potential long-term effect. During each period of plaque formation, samples were collected from the vestibular surfaces after 24 h (from teeth 15/25), after 48 h (from teeth 14/24) and after 72 h (from teeth 13/23), respectively, and evaluated for total microscopic bacterial counts (BC) and colony forming units (CFU). Microbial vitality was assessed by the plating efficiency [PE = (CFU/BC) x 100] and directly by a vital fluorescence (VF) technique. VF of 48- and 72-hour plaque was significantly reduced after Cervitec application. An inhibitory effect by Cervitec could not be discerned 12 weeks after varnish treatment.