Fruit taste is an important component of fruit quality, but its genetic basis is complex, making it difficult to alter by plant breeding. Thaumatin is a sweet-tasting, flavour-enhancing protein produced by fruits of the African plant Thaumatococcus daniellii Benth. Agrobac-terium-mediated transformation was used to produce two transgenic tomato lines expressing biologically active thaumatin in fruits. Transgenic tomato fruits from the T2 plant generation were sweeter than the controls and possessed a specific aftertaste as determined by sensory evaluation. These results demonstrate that transgenic expression of thaumatin could be useful for modifying tomato fruit taste, especially in breeding lines possessing poor fruit taste, such as those carrying a non-ripening (nor) mutation.