The effect of chewing sorbitol gum containing sodium bicarbonate on interproximal plaque pH was determined by use of an ion-sensitive field-effect transistor (ISFET) electrode system with four human volunteers. Plaque pH was lowered by 2 min of chewing of a sucrose-containing toffee. After 20 min, either sodium bicarbonate or control gum was chewed for 10 min, and the pH was followed for an additional 20 min. The minimum pH after toffee chewing was elevated by both the control gum (4.5 ± 0.3 to 5.2 ± 0.5) and the sodium-bicarbonate-containing product (4.3 ± 0.3 to 6.1 ± 0.6) to levels which were significantly different (p<0.01). The rate of rise in pH was 2.6 times faster with the gum containing buffer compared with the control gum. In comparison with the control gum, the sodium bicarbonate gum caused the pH to remain at a higher level, approximately 0.5 pH units, for 20 min after gum chewing. The addition of sodium bicarbonate to gum containing sorbitol markedly enhanced its capacity to cause and maintain an elevation of interproximal plaque pH previously lowered by exposure to fermentable carbohydrate. Sodium bicarbonate may be useful in products designed to reduce the acidogenic challenge to the teeth following food ingestion.