Objective: To evaluate the recolonization pattern of Mutans streptococci (ms) on densely colonized teeth with fixed orthodontic appliances after treatment with a highly concentrated (36%) chlorhexidine varnish. Materials and Methods: Healthy subjects (n ϭ 19) with fixed orthodontic appliances and high bacterial ms counts in saliva were recruited. In order to establish a baseline registration, plaque adjacent to brackets was sampled and cultivated on Dentocultா strips. Following professional tooth cleaning, chlorhexidine varnish was applied on all teeth for 8 minutes. The degree of recolonization with ms was assessed 2 weeks after varnish application in plaque around the brackets. For statistical analysis, the data were subjected to a repeated measures design. Results: After 2 weeks, ms counts were reduced as compared to baseline values. However, the reduction only weakly met statistical significance (P ϭ .049). Conclusions:The application of a highly concentrated chlorhexidine varnish in patients with fixed orthodontic appliances does not result in a distinct reduction of ms numbers 2 weeks after treatment.