AbstractMutations that drastically slow down fruit ripening known as ‘ripening inhibitor’ (rin) and ‘non‐ripening’ (nor) have been incorporated by backcrossing into isogenic lines of the tomato cultivar, Ailsa Craig. F1 hybrids (rin/+ and nor/+) were then produced by crossing with the recurrent parent. The rates of deterioration of fruit from the hybrid plants were compared with those from the recurrent parent and a typical glasshouse cultivar, Sonatine. Levels of acids and sugars, and also the colour, firmness and dry matter content of the fruit, were measured at two selected stages of ripeness and after storage of the ripe fruit for 10 and 20 days at 20°C. Shelf‐life of the ripe fruit was also assessed. Although the acidity fell continuously from a high value early in ripening for all four lines, during storage that in the rin/+ was better and Sonatine was worse than average. Sugar levels generally peaked close to the red stage and fell thereafter, but much variability in this component was encountered. Both cv. Sonatine and Ailsa Craig overcoloured and lost firmness during storage, but the mutant lines survived well. The results suggest that the disadvantage of a high‐quality line such as Ailsa Craig in deteriorating quickly once the fruit are fully ripe can be partially overcome through the introduction of one of the ‘non‐ripening’ alleles.