The observation of loss of heterozygosity (LOH) in tumours represents a useful clue to the presence of tumour suppressor genes (TSGs). However, analysis of this phenomenon is often complicated by tumour heterogeneity and the presence of DNA from adjacent normal tissues. The present study suggests a quantitative approach for measurement of LOH which may help to distinguish between these possibilities and to provide clues for the heterogeneous process of tumour progression. We applied this methodology to a laryngeal tumour with LOH at markers D9S171, D9S157, D8S87 and THRA1 and found that LOH at D9S171 is the commonest aberration among the tumour cells, while LOH at the THRA1 marker is present in only a small subset of the tumour cells. It is likely that LOH at D9S171 occurs early uin tumour development while LOH at the rest of the markers tested occurred later resulting in the generation of heterogeneous cell populations.