We address the question as to whether increased metalloproteinase production might be related to the high regional recurrence rate of some carcinomas, and particularly head and neck squamous-cell carcinomas (SCC). Northern blot of total RNA prepared from 26 lung carcinomas, 107 head and neck carcinoma samples and corresponding normal tissue samples demonstrates the frequent and sometimes concomitant over-expression of the 2 stromelysin genes, the type-1 collagenase gene and the pump-1 gene in the head and neck tumour tissue samples. In these SCC, over-expression of the 2 stromelysin genes and the type-1 collagenase gene (but not the pump-1 gene) is associated with a high degree of tumour differentiation. Moreover, a tumour with high levels of the stromelysin mRNAs is more likely to show high local invasiveness, suggesting that the stromelysins may be implicated in the clinical course of head and neck tumours. Evaluation of the corresponding mRNA levels may prove a useful indicator for predicting the clinical aggressiveness of these tumours.