Binary mixtures of acesulfame K, aspartame, sodium cyclamate, fructose, glucose, stevioside, sodium saccharin, sucrose and xylitol were assessed using factorial mixture designs. A simple additive model was used to generate predictions for the sweetness of the mixtures and these predicted responses were compared to the observed sweetness ratings of the mixtures. It was found that the mixtures tended to exhibit superadditivity at low concentrations, additivity at intermediate concentrations and subadditivity at high concentrations. Synergistic and suppressive effects in the mixtures were evaluated by comparing mixture responses to the sweetness ratings of 'self-mixtures'. Self-mixture data were generated by treating a mixture of a substance with itself as if it were a mixture of two different substances. Synergism was defined as a mixture response that was greater than the sweetness of the component self-mixtures, and suppression was defined as a mixture response that was less than the sweetness of the component self-mixtures. Of the 31 binary mixtures studied, 18 showed synergism, two showed suppression and 11 did not differ significantly from their components. It is hypothesized that multiple sweetness receptors or release from bitter suppression may account for the synergistic effects.