Chromosomal abnormalities in short term cultures have been investigated in 10 squamous cell carcinomas of the head and neck. Of these tumours, three demonstrated clonal chromosomal abnormalities, two showed random abnormalities and 5 patients' tumours had normal karyotypes. The 5 patients with aberrant karyotypes were all from previously treated tumours, of these, 4 patients had received radiotherapy and 1 surgery. On analysis of the three clonal tumours, two were found to be polyclonal, each with five separate clones. 116 breakpoints were demonstrated from the clonal data of these tumours, and all of the chromosomes were involved, apart from number 18. In this study we found three or more breakpoints at sites 1p36, 9q32 and 11q23. 1 of the patients investigated showed a clonal abnormality involving a breakpoint at the 11q13 site, with a further 2 patients having breakpoints at 1p22--sites previously reported to have marked clustering of cytogenetic abnormalities in oral cancer patients. Only further studies will demonstrate whether the breakpoints found are of clinical significance.