Interest has recently been directed towards the use of antiplaque mouthrinses. Most published material concerns the antimicrobial effects of these agents rather than their effects upon oral tissue. This study was conducted to evaluate the effect of a sanguinarine-containing mouthrinse called Viadent upon epithelial-like gingival cells. The cells were grown for 24 hours in supplemented Earle's medium, with and without different Viadent dilutions. Cell counts were made with a hematocytometer. It was found that 50% of the cells were inhibited at 1.2% Viadent. In similar studies, it was found that 70% ethanol and two pH buffers were less toxic than Viadent. Exposure of preformed cell monolayers to Viadent also showed significant inhibition. The relative toxicity of different antiplaque agents may be compared using such cells as a model system. In conclusion, it was observed that Viadent significantly affected gingival cell growth in vitro, that viable cell numbers were greatly reduced by short time exposure, and that the toxic effect of Viadent could only partially be accounted for by ethanol content and/or pH.