Authentic samples of commercially produced organic and conventionally grown tomatoes were collected and analysed for their 15N composition in order to assemble datasets to establish if there were any stematic differences in nitrogen isotope composition due to the method of production. The tomato dataset show that the different types of fertiliser commonly used in organic and conventional systems result in differences in the nitrogen isotope composition of this crop. A mean 15N value of +8.1 was found for the organically grown tomatoes compared with a mean value of -0.1 for those grown conventionally.