The effects of a calcium carbonate-based toothpaste with added 0.3% triclosan on the pH of human dental plaque after a cariogenic challenge with 10% sucrose solution was investigated against a calcium carbonate-based toothpaste without triclosan and an alumina-based toothpaste. A silica-based toothpaste served as a control. Twenty adult volunteers were included in this study. The results showed that the plaque pH drop and the area under the curve for both calcium carbonate-based toothpastes, with and without 0.3% triclosan, were significantly less as compared with the alumina-based toothpaste, with both parameters being least for the toothpaste with added 0.3% triclosan. Calcium carbonate has been shown in previous studies to have a buffering effect on the plaque pH after an acidogenic challenge. The addition of 0.3% triclosan to the calcium carbonate-based toothpaste seemed to enhance this effect.