In order to establish a large panel of normal and tumour DNA from primary breast cancer patients, we looked for a source of easily accessible, good quality breast tumour DNA. Following routine hormone receptor analysis at the hospital the leftover pellets contained the nuclei from the tumour tissue. We collected 670 pellets over a period of 2 1/4 years and isolated a large amount of DNA (on average 400 microg per pellet). To control the quality of this tumour DNA, we analysed 41 pellets and matching normal DNA for loss of heterozygosity (LOH), with 11 microsatellite markers along chromosome 17. This chromosome is well described for breast cancer. LOH is a sensitive method, requiring good quality and pure tumour DNA. Contamination with normal DNA will blur the results. We found a high rate of LOH, ranging from 33 to 74%, which is in agreement with other reports, and therefore recommend this rich source of breast tumour DNA for molecular biological analysis.