An eight-week, double-blind, parallel and unsupervised clinical study was conducted to compare the ability of two dentifrices, Arm & Hammer Dental Care toothpaste and Crest toothpaste, to prevent the formation of stain induced by the twice daily use of 0.12% chlorhexidine gluconate (Peridex). Stain formation was evaluated through the use of a new index (Modified Stain Index) designed to selectively detect stain of the proximal and facial surfaces of the anterior teeth. Examinations of stain formation were conducted at two-week intervals for a total of eight weeks. The results indicated equivalent stain prevention benefits for Arm & Hammer Dental Care and Crest when evaluated during eight weeks of chlorhexidine therapy. The modified stain index was shown to be valuable for discriminating location and intensity of early stain formation.