The purpose of this study was to assess the effect of rinsing and topical application of sanguinarine on labial surface plaque accumulation, compared with topically applied water, and compared with rinsing with chlorhexidine, while refraining from all oral hygiene measures for 5 days. Color photographs of the disclosed plaque were taken at the end of each phase of treatment and blindly traced using an Apple II micro-computer graphic tablet digitizer. The plaque score for each tooth was calculated by dividing the computer reading of the labial plaque surface area by the total labial surface area of the tooth. Topically applied sanguinarine showed better plaque reduction than mouthrinsing with sanguinarine. There was a significant reduction in plaque accumulation after rinsing with chlorhexidine compared with topically applied sanguinarine, water, and mouthrinsing with sanguinarine. The results of this study indicate that chlorhexidine is a more superior antiplaque agent than sanguinarine. The use of an Apple II micro-computer graphic tablet digitizer provided a valuable method for accurate plaque assessments.