This study assessed the effects on plaque in the absence of brushing of two twice-daily mouthrinses, one with an enzymatic-based formulation (Biotène) and one with an antimicrobial chlorhexidine-based formulation (Peridex), and sterile water. Plaque levels were assessed in 23 participants using a 4-day, nonbrushing plaque regrowth model after twice-daily rinsing with sterile water (negative control), the enzyme-based mouthrinse, or the chlorhexidine-based mouthrinse (positive control). Peridex showed significantly greater prevention of plaque regrowth when compared with water and the enzyme-based Biotène mouthrinse. After 4 days, the enzyme-based mouthrinse was associated with a small but nonsignificant reduction in plaque regrowth compared with water. This study confirmed that Peridex is effective at prevention of plaque regrowth. Twice-daily rinsing with a Biotène formula that contained enzymes showed a small but nonsignificant trend toward prevention of plaque regrowth versus rinsing with water.