A simplified procedure of sample preparation for the isolation of DNA (accessible to restriction fragment length polymorphism, RFLP, mapping) from wheat leaf material is presented. The procedure utilizes a sap extractor and approximately 500 samples can be processed in 1 week. The ability to handle this number of samples makes it feasible to interact with a plant breeding programme when a particularly valuable DNA marker is available. Three examples of analysing large populations are presented to demonstrate the application of the modified procedure to isolating DNA from wheat leaves.Key words: techniques, restriction fragment length polymorphism, genomic DNA isolation.